A CONCISE HISTORY OF CHEMISTRY A CONCISE HISTORY OF CHEMISTRY BY T. P. HILDITCH B.Sc. (LOND.), A.I.C. WITH SIXTEEN DIAGRAMS NEW YORK D. VAN NOSTRAND COMPANY 23 Murray and 27 Warren Streets 1911 PREFACE THIS book is an attempt to outline as briefly and succinctly as possible the historical development of chemistry, and is designed more especially for those students whose interest in this aspect of the science is stimulated by the inclusion of " Historical Chemistry " in the syllabus of examinations which concern them. It is therefore presumed that the reader is simultaneously acquiring, or already possesses, a fair knowledge of present-day chemical theory and practice, and, accord- ingly, no space is devoted to the actual explanation of hypotheses or reactions except in so far as the latter are directly bound up with the historical sequence of facts. Whenever practicable, each section is arranged so that it follows approximately those lines upon which a student would learn the simple chemical facts in question ; thus, the introductory chapters dealing with the older chemistry (down to Lavoisier) are succeeded by the history of elements and inorganic compounds, treated, as far as possible, according to the Periodic Law, whilst the details of other branches, such as organic and physical chemistry, follow in general the order given in the standard text- v books. Many facts, important in themselves but not so germane to the general development of ideas, have been collected in tabular form for convenient reference, and the 235538 vi A SHORT HISTORY OF CHEMISTRY book is concluded by a summary of the work of some notable chemists and a chronological survey of the ex- perimental and theoretical advances in chemistry during the last two centuries. In order to secure a more com- pact volume, no detailed references have been given to the literature in which the discoveries, theories, etc., were published, but the dates given in all cases will assist the student to obtain the original account of any particular point desired. I wish to acknowledge the kind help I have received from Dr. A. E. Dunstan, who read the book in manu- script ; from Dr. S. Smiles, Dr. A> W. Stewart, and Mr. H. J. Page, who aided in the correction of proofs ; and from Prof. J. N. Collie, F.R.S., who advised me with respect to the arrangement of certain parts of the work. T. P. HILDITCH UNIVERSITY COLLEGE UNIVERSITY OF LONDON CONTENTS CHAPTER I PAGE THE EVOLUTION OF THE SCIENCE i i. The Chief Chemical Epochs, i. 2. The Origin of the Science and its Name, 3. 3. Alchemy : the Ennobling of Metals, 6. 4. Alchemy : Medicinal, 9. 5. The Beginnings of Modern Inductive and Experimental Method, n. 6. Chemistry in the Phlogistic Period, 12. CHAPTER II THE CHEMICAL HISTORY OF FIRE, AIR, AND WATER ... 14 i. Fire and the " Fire Principle," 14. 2. Air : a Mixture of Gases, 16. 3. Air: its Constituents, 18. 4. Air: its "Inactive" Constituents, 21. 5. Water, 23. 6. Fire: Lavoisier's Re- volution, 24. CHAPTER III THE ULTIMATE CONSTITUTION OF MATTER 27 i. Ancient and Alchemical Views, 27. 2. The Evolution of Chemical Nomenclature, 30. 3. Discovery of Combining Proportions, 32. 4. Dalton's Atomic Theory, 33. 5. De- velopment of the Atomic Hypothesis, 35. 6. The Periodic System, 38. 7. Is all Matter derived from one ultimate Fundamental Material ? 41. CHAPTER IV INORGANIC COMPOUNDS AND THE LAWS OF CHEMICAL COM- BINATION 45 i. Chemical Affinity and the Manner of Chemical' Combination, 45. 2. The Structure of Organic Compounds, 48. 3. Val- ency, 51. 4. Electro-chemical Theories, 56. b vii viii A SHORT HISTORY OF CHEMISTRY CHAPTER V PAGE NOTES ON THE HISTORY OF THE ELEMENTS AND THEIR CHIEF COMPOUNDS 59 i. Acidic Oxides, 59. 2. Basic Oxides and Metallic Salts, 62. 3. Mineralogy, 65. 4. The Chemical Elements, 68. 5. The Metals of the Rare Earths, 73. 6. Radio-active Elements, 74. CHAPTER VI THE HISTORY OF ORGANIC CHEMISTRY 76 i. Organic Chemistry : the Chemistry of Animate Nature, 76. 2. The Earlier Theories of Structure of Organic Compounds, 77. 3. Saturation Capacity and the Modern Structure Theory, 86. 4. Benzene and the Cyclic Compounds, 88. 5. Dynamic Isomerism, 100. 6. Steric Hindrance, 105. 7. Stereo- isomerism : (a) Geometrical Isomerism, 107. 8. Stereo- isomerism: (b) Optical Isomerism, in. CHAPTER VII COMPOUNDS AND REACTIONS IN ORGANIC CHEMISTRY . . .117 i. Hydrocarbons, 117. 2. Oxygen Derivatives: (a) Hydroxylic Compounds, 119. 3. Oxygen Derivatives : (b) Carbonyl Compounds, Reactions of Condensation, 121. 4. Oxygen Derivatives: (c) Carboxylic Acids, 122. 5. Oxygen Deriva- tives: (d) Ketonic Acids, 126. 6. Nitrogen Derivatives, 127. 7. Derivatives of Elements other than Oxygen or Nitrogen, 129. 8. Heterocyclic Compounds, 131. CHAPTER VIII THE CHEMISTRY OF PLANT AND ANIMAL LIFE .... 137 i. Chemical Processes in the Vegetable and Animal Kingdoms, 137. 2. The Alkaloids, 139. 3. The Terpenes, 140. 4. Sugars and other Carbohydrates, 142 ; Glucosides, 142. 5. Amido Acids, Proteins and Purines, 145. 6. Fermentation and Enzyme-Action, 152. CONTENTS ix CHAPTER IX PAGE THE APPLICATION OF CHEMISTRY TO MANUFACTURES . . . 154 r. The Preparation of Useful Elements: Metallurgy, 155. 2. The Alkali, Sulphuric Acid, Vinegar and similar Industries, 158. 3. Some recent Electro-Technical Methods, 162. 4. Glass, Earthenware, and Cements, 163. 5. Paper, Matches, Heat, and Light, 165. 6. Dyes, 167. 7. Explosives, 170. CHAPTER X THE HISTORY OF PHYSICAL CHEMISTRY 172 i. The Physical Chemistry of Gases, 172. 2. Crystallography, 175. 3. Solutions, 176. 4. Molecular Weight Determina- tion, 179. 5. Relation of Physical Properties to Chemical Constitution : (a) Mechanical, 181. 6. Relation of Physical Properties to Chemical Constitution : (b) Electrical, 184. 7. Relation of Physical Properties to Chemical Constitution : (c) Optical, 185. 8. Photo-chemistry, 187. 9. Thermo-chemistry, 189. 10. Electro-chemistry, 191. n. Chemical Statics and Dynamics, 192. 12. The Phase Rule, 195. CHAPTER XI THE PROGRESS OF EXPERIMENTAL METHOD 197 i. Improvements in Chemical Apparatus, 197. 2. Improvements in Chemical Methods, 198. 3. Development of Analytical Methods, 201. 4. The Determination of Atomic Weights, 206. APPENDIX A BIOGRAPHICAL INDEX OF CHEMISTS 209 Alchemical Period, 209. Phlogistic Period, 210. Modern (Fundamental) Period, 212. Modern (Static Structural) Period, 215. Modern (Dynamic Structural) Period (Arranged Alphabetically), 222. APPENDIX B CHRONOLOGICAL SUMMARY OF CHEMICAL EVENTS OF OUTSTANDING INTEREST 229 INDEX OF NAMES 247 INDEX OF SUBJECTS 259 A CONCISE HISTORY OF CHEMISTRY CHAPTER I THE EVOLUTION OF THE SCIENCE § i. The Chief Chemical Epochs— History of any kind may be recorded in either of two ways : — (1) Chronologically, as a whole; (2) By taking one section of the subject at a time and treating each separate division chronologically. The first alternative is usually employed in the case of, for example, a country or province, while the second would be neces- sary in dealing with a continent composed of a variety of races, each with its own life-story. We shall find it advisable to adopt this latter plan with regard to chemistry, for the science nowadays possesses so many branches and ramifications that it is very much easier to understand the evolution of the whole from a consideration of the development of the various individual parts. There are, nevertheless, certain well-marked epochs which should be noticed in the general progress of the science. It is certain that no civilized race has yet existed in the world without giving some thought to the properties and mutual relations of the various sorts of terrestrial matter. Of course, no one can tell precisely where, when, and how chemistry really came into existence, and it would not suit our present purpose to discuss the matter at any length. ' Let it suffice to say that remote Chinese and Hindu philosophers appear to have paid attention to this branch of science, while our records i 2 A HORT HISTORY OF CHEMISTRY go back with certainty to the times of the ancient Egyptians and Greeks.1 These devoted themselves to speculations about the ultimate composition of natural substances, and at the same time — notably in Egypt — the idea of the transmutation of metals began to develop. The predominance of this notion at about the commencement of the fourth century A.D. marks the close of the first or Ancient Period — the period of philosophic speculation — and the opening of the second, the Alchemical Epoch. This lasted for more than a thousand years, and it is said that even in the last century there yet existed individuals holding alchemical tenets ; practically speaking, however, the ideals of chemists underwent a profound change towards the close of the seventeenth century. Alchemists were dominated by two pre-conceived and extraordinary ideas : firstly, that it was possible to change common metals into gold by a chemical process ; secondly, that the change was to be accomplished by I the agency of a substance, known variously as The Essence, ' The Philosopher's Stone, The Elixir of Life, etc., which pos- sessed entirely supernatural powers. The development of the physical sciences, on the other hand, had been uncommonly rapid during the seventeenth century, and this was largely due to the adoption of induc- tive methods. It is thus easy to see how chemists, tired of fruitless search on a vain quest, and sickened by the duplicity which was too frequently practised, turned to new methods. Robert Boyle in particular changed the trend of chemical reasoning, and thereby rendered his greatest service to science. In the next period — the Phlogistic Period, dating from about 1700 to 1775 — the properties of the most various bodies were examined with a view to classification. The property which attracted most attention was that of combustion — so much so that this era fittingly takes its name from the famous but incor- rect theory designed to explain the phenomenon of burning. 1 Berthelot's " Les Origines d' Alchemic " is a standard work for those wishing to study in detail the earliest era of the science. THE EVOLUTION OF THE SCIENCE 3 In 1777 Lavoisier published his theory of combustion, worked out by the help of the balance, and made possible by Scheele's and Priestley's discoveries of oxygen ; this inaugurated the era of modern chemistry, which may again be subdivided into three periods : — (1) The Fundamental Period, comprising the labours of Davy, Dalton, Gay-Lussac, Berzelius, Dulong, Faraday, etc. (2) The Period of Static Structural Chemistry, commencing with Wohler's synthesis of urea in 1828, and comprising the foundations of systematic organic and physical chemistry. (3) The Period of Dynamic Structural Chemistry, i.e. the development of the most recent views concerning the ultimate composition of matter, the structure of chemical (and par- ticularly " organic ") compounds, the nature of electrolysis, etc. This period may be said to have commenced about 1880. We may, then, summarize the six periods of chemical history in the table on page 4, giving at the same time instances of familiar historical events which may serve in some measure to correlate the various dates. § 2. The Origin of the Science and its Name— There are various indications that some knowledge of the practical applications of chemistry existed long before the era of Western civilization. The Chinese, for instance, possessed means of manufacturing articles which in some cases cannot be made with the same degree of elegance at the present day ; this implies a considerable acquaintance with some sort of technical chemistry. At a less indefinite date, which is still too remote to be fixed with any certainty, we find the Phoenicians and Egyptians well acquainted with the manufacture of glass and pottery ; some of the simpler metallurgical processes were already practised, in- cluding the mechanical separation of gold, the smelting of iron, the preparation of mercury from cinnabar, anjd the separation of lead and silver. The arts of dyeing and embalming were also 1 1 largely engaged in by the Egyptians. The Jews, too, in the x ' A SHORT HISTORY OF CHEMISTRY .1 i S « ft, ^ 1 fcj i "^ dria. dria line of Greek an ilosophy. at Alexand of Alexan by Decl phi Fire Sack C w iS'rt 6-° W •Htf G 5 .5 o l-^l1 «2J« v« JQ <« <« O^J O O 1111 5-5 $ 2 n3 C .2 £ •S x 2,0 g^ S^3 ^<«OS S § I I I! C o £ C Q fe cn up r^io o ^- M N N O °0 T}- IO y-, • q Q 2 •a 1 i *3 o & C 3 OT e ~ ° I w 'i 1- g I c ti c 3 rt >^ fa cw Q THE EVOLUTION OF THE SCIENCE 5 reign of Solomon (and probably for some time prior to that period) rec jgnized at least six distinct metals : gold, silver, iron, copper, tin, and lead. Metallurgy at this early date was carried on chiefly in the northern part of Egypt ; deposits of ores were fairly abundant in that region, and, in addition, the seaport of Alexandria afforded means for the import of ores from the various lands washed by the Mediterranean. Not infrequently metallic de- posits, consisting of a mixture of metals or ores, would be found ; sometimes much lead accompanied by a little silver, sometimes silver and gold together, sometimes other metallic mixtures. Moreover, methods were soon devised for preparing the "noble" from the "base" materials in such instances; what is more natural, then, than that the idea of the baser being transformed into the rarer metals should gradually come into the minds of these early metal-workers? Here is the origin of the transmutation theory ; gold and silver were re- garded, then as ever, as most precious and valuable ; mixtures of these with common substances were found — perhaps Nature was slowly transforming the base into the rare ? This sugges- tion developed into a most persistent and dominating belief in the alchemical period ; and even now, centuries after the theory has been dropped, we retain in common use phrases which betray an innate leaning towards alchemical ideas, such as " base " and " noble" metals, "perfect " gases, etc. The famous transmutation theory, then, probably arose from a very superficial kind of reasoning, and this may be due to the circumstance that the early metallurgists do not appear as a rule to have been in touch with the " philosophers " or learned theorists. The latter class of men, naturally most prominent in ancient Greece, had little in common with the former. It is convenient to summarize at this point the chemica knowledge of the ancients : — (i) Practical. — In China and India (?), in Phoenicia and Egypt : metallurgy, dyeing, glass, earthenware. 6 A SHORT HISTORY OF CHEMISTRY (2) Theoretical. — In Greece (500-200 B.C.) and Rome (100 B.C.-A.D. 150); vague, general observations on nature. (3) Experimental (according to the modern meaning of the word). — Practically none. With regard to the origin of the word " chemistry," there is a choice of about six very plausible " derivations," such as from the North Egyptian word " chemi " = Egypt ; from ^ 77 //, c t a = Egyptian art; from x >///,€ to, = black, etc. As these cannot all be correct, let us be content merely to say that the first use of the word " chemia " appears in an astrological treatise com- piled by Julius Firmicus, a writer of the fourth century of the Christian era. § 3. Alchemy : the Ennobling of Metals — When we turn to review the next period of chemical history, it at first appears as if the Greeks had all the clear-sighted theories and the alche- mists none, for the superabundance of views and metaphor are bewildering. There is a break of some 200 years between the latest philosophical writings and the earliest authentic alche- mical works, and during this time a great change in view-point took place, culminating in the predominant belief in " trans- mutation," which appears as a well-known doctrine in all the latter treatises, although it is scarcely mentioned in the former. This is natural in view of the probable origin of the theory (p. 5) and of the fact that the old philosophy finally died out after Hypatia's murder, and was replaced by a system based on the Christian religion. The unscrupulous blending of Christian hypotheses and natural science led to as dismal consequences to both as the intolerance of Christian authorities to science has done in many an instance. Assuming that they possessed by revelation a divine " scheme " of the moral universe, the new race of thinkers extended it to the material world, and deduced that simplicity was the key-note and perfection the end of matter as well as of mind. Gold and silver were as- sumed the most perfect metals, " the end of Nature in regard to metals," and the original aim of alchemy was to "assist THE EVOLUTION OF THE SCIENCE 7 Nature " by the application of certain agents or medicines, which, acting on the " baser " metals, should purge away the impurities and leave worthier members of the metallic state. Much later the idea arose that such agents — especially the greatest of all, the Philosopher's Stone, Alkahest, Elixir, etc. — ought to be of service to men's as well as metals' ills; and iatro-chemistry, in which chemistry is looked upon as the servant of medicine, was developed. This branch of alchemy, and the alchemical theories of the ultimate constitution of matter, are discussed later (pp. 9, 28). Because of the universal desire for gold and silver, and the ease of making alloys or amalgams bearing strong superficial resemblance thereto, the aim which alchemists set before them, albeit at first purely philosophical, naturally lent itself to decep- tion, and alchemy quickly became degraded into a mere gold- imitating art. Various popes and princes therefore proscribed its practice in their realms, but usually found it too valuable a means of filling empty, purses to be very severe on its adepts. Consequently nearly every European court had its private alchemist, who in general was merely a swindler, not a scientist, with whom matters went hard in case of detection, but who usually found it sufficiently easy to secure against such a con- tingency and to make a comfortable living. For a long while, indeed, true chemists were few and far between, till better ideals once more arose, thanks in the main to the outspoken utter- ances of Boyle, Kunkel, and others. With -the charlatans we are not concerned, but proceed to summarize as far as we can the general trend of theory — a difficult task, since, to a greater extent than at any other period, each followed his own in- dependent path. Nearly all alchemical writers refer to one Hermes Trismegis- tus as the father or originator of alchemy. This somewhat mythical person was supposed to have developed very largely the practical side of alchemy in Egypt at an indefinitely remote period ; his existence (except in the minds of these writers) is a 8 A SHORT HISTORY OF CHEMISTRY matter of doubt, but his name has certainly survived, even in the chemical parlance of the present day. It is amusing to note how, later on, devotees of the " hermetic art " in their anxiety to invest their science with a touch of religious sanctity asserted that the first of their cult were Biblical characters, such as Adam, Tubal-Cain (" an instructor of every artificer in brass and iron "), Moses and Miriam, or Job (" Thou shalt lay up gold as dust ") ! In reality the science of alchemy was chiefly fostered in the museum of Alexandria l in the first centuries of our era, under both heathen and Christian teachers, as Zosimos of Panopolis (circa A.D. 420-450) and Bishop Synesius (circa A.D. 400) until the decay of the Western Roman Empire and the advent of the Arabs, i.e. until about A.D. 640. The Arabs took up science with wonderful zeal, for within a century universities, which soon became famed for mathematics, medicine, astronomy, and alchemy, began to spring up in Bagdad, Cordova, Seville, Toledo, and elsewhere, and to these in the course of the next four cen- turies came many Western European students. Geber is the first alchemist of note whose existence is authentic, and of his actual life we know very little, except that he was an Arab physician, whose reputation lasted down through the Middle Ages. No other Mohammedan alchemist attained such fame as he, and he wrote several works on chemistry, which still exist in the form of Latin translations. When Arab learning declined (about 1200) alchemy was propagated in England, France, and Germany by the students mentioned above, and indeed was fully developed in Western Europe by the year 1400. It was 1 The " Alexandrian Academy " was founded as a school and library by Ptolemy Soter, destroyed by fire in 47 B.C. and A.D. 216, and taken by the Arabs in 642. It is interesting because (i) it must have acted as a point of contact for Greek theorists and Egyptian metal-workers, (2) it was the final seat of the old heathen philosophy, and although the Christian authorities murdered the latest of the philosophers, Hypatia, in their jeal- ous endeavours to stamp it out, enough of their writings must have been left to enable the Arabs, some two hundred years later, to assimilate and propagate science as known to Hypatia, and her disciples. THE EVOLUTION OF THE SCIENCE 9 carried on notably in "apothecaries' shops," which, designed for the purpose of preparing the simple medicines then used, served also to train numbers of keen alchemists. The fact that chemistry in the Middle Ages was dominated by mediaeval religion will account for many of the biassed, prejudiced ideas which held sway, and the influence of the desire to make gold and the belief in the possibility of trans- mutation all helped to enshroud the real end of the science in a mist of preconceived notions and a tangle of hopeless beliefs. Yet it must not be supposed that this period of chemistry was unfruitful. Indeed it has been very well said that the hunt for the Philosopher's Stone and unlimited gold resembled very much the search of the sons of the man who said on his deathbed that there was a fortune buried in his vineyard — and we, the des- cendants of the alchemists, are still reaping the benefit from the fertile discoveries these made in the course of so much mis- directed ploughing. § 4. Alchemy : Medicinal — While the philosopher's mind was fixed on one theme — gold manufacture — his experiments were naturally concerned only with metallic derivatives, so that few of the new facts discovered related to any but this class of compounds. When the Renaissance of learning and the Reformation led to a wider intellectual outlook the scope of chemists' views also appeared to broaden, and a larger field of use for chemistry was opened up. Originally the doctrine of the ennobling of metals had been deduced by analogy (however fanciful) with human moral development, and now, conversely, the beliefs (for theories were to alchemists "articles of faith") which had arisen as to the composition of metals were applied to the healing of physical disease. Basil Valentine and a few other workers of the first alchemical period here and there applied isolated metallic preparations as medicinal remedies, but Paracelsus (sixteenth century) was the first to emphasize the close inter-dependence and alliance of chemistry and medicine. He assumed that the three " principles," sulphur, salt, and ib A SHORT HISTORY OF CHEMISTRY mercury, which were held to constitute the different metals, also composed the human body, and that illness was the result of deficiency or excess of one or more of these in the organism — an assumption which was characteristically accepted as a creed by Sylvius, van Helmont, Tachenius and other alchemists of the next few generations. The " medicine of the third order," the Philosopher's Stone, which should bring perfection to weak and erring metals, was naturally supposed to perform the same function for mortals, endowing them with an indefinite span of life and resistance to all physical decay. This fusion of medicine and chemistry was of advantage to both, but par- ticularly to the latter, which then attracted men of wider culture than previously ; it led to the discovery, too, of further new facts and compounds, especially in the domain of what is now " organic " chemistry, and unintentionally paved the way for the emancipation of chemistry from a gold-making art to a truth-seeking science. At the present day there exist in nearly all civilized coun- tries societies for the extension of chemical science and numer- ous periodicals devoted to the same purpose ; but in alchemical times there was nothing of this kind, and the isolated character of each individual's work is very conspicuous. (Cf. Appendix, pp. 209, 210.) In the earlier history of alchemy this independence was due to the selfish, competitive motives aroused by the quest for gold and the Philosopher's Stone. Later on the change to iatro-chemical ideals, which postulated health for all rather than wealth for one, and the repeated failures to obtain the " elixir," which aroused a feeling that united work might solve problems which baffled isolated workers, caused the formation of various alchemical unions. These were chiefly " secret societies/' and they thrived from about the beginning of the seventeenth to the middle of the eighteenth century, but were in no way compar- able to or connected with the real scientific societies then existing, such as the Royal Society of London (founded 1663). THE EVOLUTION OF THE SCIENCE ti Alchemy consisted, then, in the later stages of its existence, of two branches, the one concerned merely with gold manufac- ture, the other with the application of chemistry to healing. The latter side of the subject cannot be said to have been abandoned, but rather to have been extended by the rapid adoption of the inductive method of research, its development in one direction (the phenomena of combustion) leading to the doctrine of phlogiston, which characterized the next period of chemical history. The efforts to make gold from baser metals were so unsuccessful, and yet afforded such scope for duplicity and charlatanism, that a great deal of scepticism arose in course of time as to the possibility of metal-transmutation at all, and gradually the idea died out. It might be pointed out that, until definite proof was given for regarding the metals as ele- ments (i.e. in Lavoisier's time), it was not chemically wrong to believe in the possibility of changing one into another. § 5. The Beginnings of Modern Inductive and Ex- perimental Method — One of the first to apply the " induc- tive " method to chemistry was Roger Bacon (thirteenth century) ; then, towards the end of the seventeenth century, the necessity of putting aside the subsidiary aims which chem- istry might serve seems to have been more widely felt, and the efforts of chemists were directed along new lines, notably by the work of Boyle and Kunkel. The latter, himself an enthu- siastic alchemist, was concerned more particularly with the careless phraseology and frequent duplicity of his contempo- raries, and denounced both with considerable vigour. Boyle's writings, however, show that he had little faith in alchemy, but possessed views on the nature of chemical combination and of chemical elements which have stood their ground ; moreover — and this is very noteworthy — he stated that experimental methods and careful observation were the only sure paths to development. The general adoption of these views, although hampered for a time by neglect of quantitative investigation, has undoubtedly been the cause of the rapid progress of the science to its present position. 12 A SHORT HISTORY OF CHEMISTRY Let us contrast, then, the three different methods of investi- gation which we have now discussed. The ancients based their theories on careful observation of natural phenomena, but made no experiments to shed further light on their assumptions. The alchemists based their theory on one fundamental assumption (the simplicity and unity of nature), and made many experiments to show that the theory was certainly true. The modern inductive method, which chemists owe especi- ally to Boyle, is to base a theory on a consideration of the known facts, thence to design new experiments to throw fresh light on the subject, and, from the new facts so discovered, to modify or confirm the original theory, and then repeat the process indefinitely. The whole difference of the systems lies in the different relations which the various ages assigned to the bearing of ex- periment and observation on theory. § 6. Chemistry in the Phlogistic Period — It has been necessary to give a detailed account of the chemistry of the alchemists and ancients, because their view-points differed fundamentally from those of all later investigators. Chemistry, indeed, as understood at present, originated when alchemy de- cayed and the attainment of chemical truth was made the goal of the science. The phlogistic chemists form a kind of link between old and modern workers, for they aimed at the ex- tension of chemical knowledge, while their theories and methods were often not far in advance of those of their predecessors, the alchemists. We will therefore conclude this sketch of chemical evolution by a resume of the work done by the phlogistonists, and then pass on to the history of the various branches of chemistry. In the phlogistic period we notice first of all that qualitative investigation was the almost invariable rule — the use of the balance being quite exceptional. The chief subject of experi- ment was the phenomenon of combustion, usually explained THE EVOLUTION OF THE SCIENCE 13 at that time on the "phlogiston" hypothesis (cf. chap, ii., P- 15)- Much progress was also made with methods of qualitative an- alysis, and during this epoch the composition of water (Caven- dish) and of air (Mayow, Priestley, Scheele, etc.) was cleared up. In consequence of the manipulative processes intro- duced by Boyle and (in lesser degree) the later iatro-chemists, the investigation of gases went on rapidly and the isolation of nitrogen or " phlogisticated air " (Rutherford, Scheele, Priestley), oxygen or " dephlogisticated air" (Scheele, Priestley), car- bon dioxide or " fixed air " (Black), hydrogen (Cavendish), and chlorine (Scheele) among other gases may be placed to the credit of the " phlogistic " chemists. The mutual relationship of salts, acids and bases was also recognized, Rouelle (1744) de- fining the former as a combination of the two latter, and also distinguishing between neutral, acidic, and basic salts. The more ordinary acids became fairly well-known, sulphuric, phos- phoric, nitric, and hydrochloric acids being classified as " mineral acids," while formic, citric, oxalic, uric, tartaric and others were termed " animal acids " ; bases such as the alkalies and alkaline carbonates, and " earths " such as the calces of magnesia alba, alum, barytes, quartz, etc., were also characterized at about this time. In what is now called organic chemistry, the pre- paration of alcohol, wood spirit and various " ethers " was advanced, while Scheele, who discovered most of the " animal acids " just mentioned, also isolated glycerine from fats. Technical chemistry now rose to be an independent branch of the science, the following being the more notable develop- ments of the period : the manufacture of nitric, sulphuric, and Nordhausen sulphuric acid ; the metallurgy of zinc, and pro- cesses for gilding and silvering metals ; the fabrication of por- celain (Sevres) ; and of mineral dyes and paints, such as Prussian blue (Fe4"i[Fe"(CN)6]3) and Scheele's green, CHAPTER II THE CHEMICAL HISTORY OF FIRE, AIR, AND WATER § i. Fire and the "Fire Principle "—Of the four "Aris- totelian elements " it may be said that, while chemists always have been and will be concerned with the constituents of earth, the nature of fire, air, and water was practically cleared up in the course of a century, or, more precisely, during the phlogis- tic period. It is thus convenient to study these three together at this point. It was the universal custom of the ancient philosophers to consider all three as elements, but it must be re- membered that " element " at that period meant rather a funda- mental property, than a fundamental unitary kind of matter. Later on, some of the alchemists held that by interaction of pairs of these four elementary properties, three fundamental principles, akin to mercury, sulphur, and salt, were formed. It is easy to see why " fire " was given a position equal to the other three elements, for while the gaseous, liquid, and solid states could be repre- sented fundamentally by air, water, and earth, the equally patent state of "flame" was supposed to be the manifestation of the principle of " fire ". The earlier alchemists did not turn their attention very seriously to the problem of combustion, but in the iatro-chemical era, Sylvius (circa 1650) suggested that sulphur (the alchemical " principle ") was the principle of fire, and also drew attention to the analogy between burning and breathing. This suggestion was accepted by other alchemists, such as Homberg and Kun- kel ; Boyle, who, to use the title of one of his works, was more of 14 THE CHEMICAL HISTORY OF FIRE 15 a " sceptical chymist," regarded it as possible, but not proved, and preferred merely to call the fire principle a " combustible earth ". In the meantime Mayow (1668-9) showed that there was a substance in air which took part both in the calcination of metals and in respiration, but did not seemingly pursue the subject far enough to give a complete explanation. At about the same date the alchemist Becher was trying to revive the old " principles " under new names, " mercurial, vitreous, and combustible earths " ; the latter, " terra pinguis," was set free when combustion or calcination took place. Unfortunately, as has frequently happened, preconceived assumption met with more notice than precise observation (due in this case to Mayow), and Stahl, one of Becher's pupils, elaborated Becher's idea into the famous phlogiston theory. Stahl assumed that all combustible or calculable matter con- tained a substance "phlogiston " * which was evolved during the process of burning ; the more readily and completely com- bustible the substance, then, the greater was the amount of phlogiston it contained. Coal was supposed to be particularly rich in phlogiston, for on heating it is almost entirely burnt away, while by heating it with many metal oxides the metal is reformed. On the other hand, the metals, etc., were supposed to be the products of union of phlogiston with the metal calces, and we can represent these views by an equation, perhaps, as follows : — Metal ^ Phlogiston + metal calx (oxide). Sulphur ^t Phlogiston + sulphuric acid. Phosphorus ^> Phlogiston + phosphoric acid. When a calx or sulphuric or phosphoric acid is heated with matter rich in phlogiston (coal), the metal or sulphur or phos- phorus is " revived ". This idea is a direct inversion, so to speak, of our modern view of combustion, for we hold that 1 Some consider that " phlogiston " has been in a manner realized in the form of the " heat of formation or decomposition " of a body. 1 6 A SHORT HISTORY OF CHEMISTRY addition of oxygen takes place in combustion, and elimination of oxygen in reduction. In order to make the relation of phlogistic to modern views quite clear, we may add that : — Elimination of phlogiston = oxidation (combustion). Addition of phlogiston = reduction (elimination of oxygen). Stahl suggested that a similar explanation, based on phlogiston, could be found for respiration, which would thus consist of an exhalation of phlogiston. This theory gave a concise explanation of a large number of miscellaneous facts, and it was exceedingly simple. Unfor- tunately, it was also hopelessly impossible ; the " elimination of phlogiston " was invariably accompanied by gain in weight, and conversely ! This did not deter the earlier adherents of the theory, at all events, from accepting it as blindly as did the alchemists the doctrines of metal transmutation and the exist- ence of the elixir of life. One cannot quite understand the attitude of chemists who said that " although " gain in weight always accompanied combustion, and loss in weight what we now call reduction, yet " notwithstanding this " the former phe- nomenon was due to loss, and the latter to gain, of phlogiston. Of course little attention was paid at that time to quantitative methods, and the importance of mass as the only reliable guide to the " amount of matter in a substance " was unrealized ; but even much later, phlogistonists suggested, as a way out of the difficulty, that their fire-stuff possessed a negative weight. That the phlogistic theory was in no wise a worthless attempt at an explanation of combustion is proved by the number of useful discoveries made in all departments of chemistry in the - eighteenth century and by the men whose allegiance to it did not prevent them from being brilliant chemists (Black, Cavendish, Priestley, Scheele, Bergman, etc.). The nature of air and water, indeed, was finally elucidated during this epoch, and it will be most convenient to deal with these before proceeding tO;give a de- scription of the advent of Lavoisier and the decline of phlogiston. § 2. Air: a Mixture of Gases — For long ages people THE CHEMICAL HISTORY OF AIR 17 were content with the old notion that air was an " element," a simple substance, but in course of time two circumstances combined to render this view open to question. (1) Van Helmont, whom many regard as the " founder of pneumatic chemistry,'' showed that it was possible to isolate" gases from various materials, and that these gases frequently possessed varying properties. He, indeed, was the first to use the term " gas " (geist = spirit), and differentiated " gases," which he supposed to be unliquefiable, from " vapours," or gases which on cooling condensed to the liquid state. He seems to have isolated carbonic acid in various ways (com- bustion, fermentation, etc.), and gave specific names to a number of other gases, but we cannot tell in many cases to which particular substance he refers. (2) A little later (1650-90) the behaviour of substances heated in an enclosed volume of air began to be observed ; Mayow (1668-9) noted that when metals were calcined or animals breathed, a part of the air (the " spiritus nitro-areus" also a constituent of saltpetre) was used up, while the remainder (" nitrous air ") was somewhat lighter than the original air, was insoluble in water and did not support combustion. Similarly Boyle's work on calcination and respiration showed him that air was a mixture and that only one part of it was actually essen- tial to burning or breathing, but neither he nor Mayow definitely prepared this active ingredient. The fact that air itself is ponderable was first proved by Rey (1630). These facts comprise practically the whole knowledge of air down to the middle of the eighteenth century. The phlogistonists regarded it simply as a receptacle into which phlogiston escaped in cases of combustion, etc., and if it was desired to explain the incapability of some gases to support life or flame, did so by the assumption that such were already " phlogisticated," — saturated with phlogiston. Little material progress was made till later upholders of the phlogistic theory (Black, Priestley, Scheele, etc.) devised means for separating, 1 8 A SHORT HISTORY OF CHEMISTRY collecting, and manipulating gases which rendered their more minute investigation possible. Priestley, for instance, introduced the familiar "pneumatic trough " and "beehive shelf" and also utilized mercury, instead of water, as the collecting medium. We may thus say that at about 1750 air was believed to be a mixture of at any rate two ingredients, one which supported life and one which did not, or was a gas " partly saturated with phlogiston ". § 3. Air : its Constituents — The bulk of the work of the later phlogistonists on air was of a qualitative nature, but excep- tions are to be noticed in the case of Joseph Black's work on carbonic acid (1750-5) and Cavendish's analysis of air and water (1785 onwards). The crucial point of the problem was reached when Scheele and Priestley simultaneously and inde- pendently discovered oxygen in the summer of 1774. Both of these were examining the gases*' evolved from the " calces " of metals under different conditions, and both obtained oxygen by heating red oxide of mercury, and noted that it supported combustion similarly to air, only very much more vigorously. Their adherence to the phlogiston theory prevented them from arriving at the correct explanation of combustion, but they re- cognized that air was a mixture of two different gases. Scheele also obtained the new gas by heating saltpetre alone, and by warming black oxide of manganese with phosphoric or sulphuric acids ; he called it fire air. Priestley obtained it from minium (Pb3O4) as well as from mercuric oxide, and named it de- phlogisticated air, from the readiness with which it " absorbed phlogiston ". By finding an absorbent for the new gas (Priestley (1775) used "saltpetre gas," nitric oxide, and Scheele (1777) ferrous hydrate or phosphorus) both proceeded to isolate the other constituent of air in a tolerably pure state, and found it to be somewhat lighter than air and a non-supporter of com- bustion, thus confirming Mayow's previous work (p. 15); it should be noted that the existence of oxygen itself was practically discovered by Mayow and by Boyle, although neither succeeded THE CHEMICAL HISTORY OF AIR 19 in its isolation. This inactive part of the air, which Priestley termed phlogisticated air, and Scheele spent air, had also been isolated a little earlier (1772) by Rutherford, who adhered to Mayow's name, nitrous air. A number of other scientists also worked on this gas at about this period, and it acquired a variety of names, Fourcroy in 1788 and Berthollet in 1791 showed it was a constituent of animal tissues, and the former author, from its relation to the " alkaline " ammonia, suggested the name alcaligkne ; Lavoisier used the term mephitic air and later azote — a name which means the same as the German Stickstoff (suffo- cating substance). Its modern name, nitrogen, was first used by Chaptal, on account of its relation to nitre. It should be noted that the elementary character of the gas was not realized at this time, nor indeed for a considerable period after, for Davy and Berzelius believed it to be made up of oxygen and another element — a view which was not finally abandoned till about 1 820. We must now consider the other constituents of air — carbonic acid, water, and the " rare gases of the atmosphere ". The presence of carbonic acid was appreciated even before Mayow's time, for van Helmont (early part of the seventeenth cen- tury) noticed its occurrence in air, in caves, in mineral springs, and in animal organs, and showed how to prepare it by burning coal, fermenting wine or decomposing chalk or " potashes " with vinegar. He called it gas sylvestre, but confused it with other gases which do not support combustion. Black (1750-5) also realized its presence, and called it fixed air, but we must discuss his work somewhat later, as it is concerned with the com- position of the alkalies and alkaline carbonates rather than with that of air. Lavoisier (1775-6) and Dalton (1803) both deter- mined with more or less accuracy the proportions of carbon and oxygen present in the gas, but this we can also deal with more appropriately in a later chapter. We should mention, however, that Scheele and Priestley each showed that when a candle burns in an enclosed air-space, exactly as much fixed air is generated as dephlogisticated air is consumed. A SHORT HISTORY OF CHEMISTRY It has already been said that Cavendish was one of the few chemists of the phlogistic period who concerned themselves with quantitative research, and as a matter of fact, he made some exceedingly accurate analyses of air, showing that its com- position was practically constant, but varied within very small limits. He estimated the oxygen by explosion with hydrogen, and then to see if the residual phlogisticated air was homogene- ous, sparked it with excess of oxygen till no further contraction took place. He stated (1785) that " if there is any part of the phlogisticated air of our atmosphere . . . which differs from the rest ... we may safely conclude that it is not more than TJT_ part of the whole ". A hundred and ten years later it was proved by Lord Rayleigh and Professor Ramsay that a little less than one per cent of the atmosphere was made up of a series of " inactive," chemically inert, gases. We will summarize the knowledge of air gained by the end of the phlogistic period and then return to the description of these "new " gases:— PERIOD : Ancient, Al- chemical. & Modern Name. Oxygen Definitely Isolated. 1774 Nitrogen 1772 PHLOGISTIC. Phlogistic Names. Regarded as — Fire air (Scheele) Air Dephlogisticated air devoid of (Priestley) phlogiston. Spiritus nitro-asreus (Mayow) Spent air (Scheele) Air Phlogisticated air saturated with (Priestley) phlogiston Nitrous air (Mayow) (Priestley), or Mephitic air, Azote Nitric acid (Lavoisier) saturated with Nitrogen (Chaptal), phlogiston etc. (Cavendish). Carbonic acid About 1620 Gas sylvestre (van or earlier Helmont) Fixed air (Black) Water Various, e.g. Phlogisticated muriatic, nitric, or sulphuric acid, An elemc. THE CHEMICAL HISTORY OF AIR . 21 § 4. Air : its " Inactive " Constituents— The history of the five " inactive gases of the atmosphere " is comprised within a very recent period — the last fifteen years ; and much of the work of their discovery, curiously enough, was carried out within a few hundred yards of the house in Gower Street, London, in which Cavendish, the last previous worker on the subject, lived a century before. The isolation of argon, the first of the series to be recognized and also the most abundantly occurring mem- ber, was due in the first instance to physical research, Lord Rayleigh (1893), who was engaged in checking the densities of the principal gases, observing that nitrogen from the atmosphere was always slightly heavier than that prepared from chemical compounds. He and Ramsay found this was not due to any peculiarity of the nitrogen present in either case, and therefore set out to repeat Cavendish's work on the question of the homogeneity of nitrogen — only with all the advantages of modern appliances and methods. The meaning of the last sentence may be realized when it is reflected that these later investigators had at their command (a) spectrum analysis, where- by traces of any gas could be qualitatively determined with the greatest ease (cf. chap, x., p. 186) ; (ti) methods for cooling air sufficiently to liquefy it, whereby huge volumes of gas could be treated at once (cf. chap, x., p. 174); (c) chemical means of absorbing nitrogen and other gases which were unknown in Cavendish's time. They found, by repeating Cavendish's ex- periment of sparking the residual gas with oxygen over potash, and also by passing nitrogen repeatedly over heated magnesium or calcium, that a residue of inert gas, giving an altogether new spectrum, was left. This they termed argon, from its incapability of entering into chemical reactions. It was known that a gas, supposed to be nitrogen, was often found occluded in uranium minerals (cleveite, brb'ggerite, pitch-blende, etc.). These were next examined by Ramsay and from them in 1895 he obtained another inactive gas much lighter than argon, previously only observed in the sun (by Sir N, 22 A SHORT HISTORY OF CHEMISTRY Lockyer, who christened it helium, in 1868), and at once re- cognized by its spectrum (with a notable yellow line — " D3 "). Argon was also sometimes obtained, one mineral — malacone — giving this as the chief occluded gas. The residue from air termed "argon " was therefore prepared in large amount in 1898 by Ramsay and Travers and fractionally distilled at very low temperatures ; two main fractions were obtained, and of these, the lower boiling one gave by repeated distillation two gases, helium and another new member, neon, while the other consisted mainly of pure argon with two heavier gases, krypton and xe?ion. There was thus obtained a series of five new gases of unprece- dented nature, in that they seemed to be devoid of all chemical affinity, no compound of any of them being known. Their physical constants have been determined fairly fully and are given in the table below ; the atomic weights are determined from the densities, for Ramsay found by the method of Kundt and Warburg (cf. p. 189), that the ratio of specific heat at constant pressure to that at constant volume was about i'6o in all cases, the gases being accordingly monatomic. The spectra, boiling-points, melting-points, etc., have also been determined by various workers, notably Ramsay, Travers, and Dewar ; helium was not liquefied for some time, but Kamerlingh Onnes finally succeeded in condensing it by the Linde-Hampson process (p. 174), in 1908. Careful search has been made by Moore in Ramsay's laboratory for members of the series heavier than xenon, but without success (1908). The table shows, as well as the physical properties, the approximate amounts of each pre- sent in air, from which it will be seen that the designation " rare gases of the atmosphere " is not very apt, since together they comprise almost one per cent thereof, besides occurring oc- cluded in various minerals, and dissolved in many springs, etc. Their relation to the problem of radio-activity is not yet com- pletely understood, but it may be said here that Ramsay has proved that helium at least is one of the disintegration products of radium, and that " radium emanation " is a gas possessing the properties of a higher mernber^of the series, THE CHEMICAL HISTORY OF WATER 23 Percentage in Atomic Weight Boiling- Melting- Name. Atmosphere. (1910). point point. (760 m.). Helium 0-0005 4-0 4-5° abs. Below 3° abs. Neon 0-0025 20-O - 243° C. -253°C. Argon 0-942 39'9 - i86-i°C. - 189-6° C. Krypton O-OOO02 83-0 - 1517 - 169-0 Xenon Less than any 1307 - 109-1 - 140*0 of the above § 5. Water — The story of water is a much simpler one than those of either air or fire. From the earliest times right down to the end of the phlogistic period (and, in isolated in- stances, even later) it was looked upon as an " element ". The ancients seem to have thought that water and air could be transformed into each other, and also that water was readily converted into " earth " — another proof that " element " did not then mean a definite unitary species of matter. The latter idea crops up persistently through the next two periods : thus Basil Valentine, who realized the importance of water to plant and animal life, held that it was transformed in the organic economy into earthy matters, and amongst the phlogistonists we find Scheele engaged in a qualitative analysis of the solids left by evaporation of water (he mentions lime and silica as the chief), while Lavoisier's first purely chemical service was to show that such solids were either primarily dissolved in the water, or dissolved by it out of the containing vessels. We owe the discovery of the compound nature and quali- tative composition of this all-important liquid, however, to Cavendish, who proved definitely that when hydrogen burns, water is the sole product of combustion. And here we may conveniently recount the history of hydrogen. The gas and its formation from iron and dilute acids were known to van Helmont, who seemed to confound it with carbonic acid. Its Inflammability had been observed by others of the later al- chemists and by Boyle ; its reducing properties caused not a few of the phlogistic chemists to look upon it as phlogiston itself. The liquid formed when it burned was usually believed to bg 24 A SHORT HISTORY OF CHEMISTRY an acid until, as just mentioned, Cavendish (about 1782) showed this to be pure water. He proved that hydrogen (or inflam- mable air, .to use his, phlogistic term) was only explosive in presence of air or oxygen, thereby pointing out the remaining constituent of water, and he determined the relative weight of the gas with moderate accuracy. Although Cavendish used hydrogen in determining the composition of air, it was Lavoisier who, in 1783, made the first quantitative synthesis of water. Lavoisier (1787) also gave hydrogen its modern name ("water- producer "), and showed how this gas could be formed by the action of steam on red-hot iron. The direct quantitative analysis of water came a little later, when Nicholson and Carlisle succeeded in decomposing it by electrolysis (1800). The true composition of water, then, became known at about the beginning of the nineteenth century, but the notion of its elementary nature died very hard, even Priestley remaining unconvinced for some years. § 6. Fire : Lavoisier's Revolution — In following up the history of air and water we have been forced to make a digres- sion from that of combustion, which it will be recalled had been traced down to the time at which the phlogistic theory held full sway. We must now return in point of time to the years immediately preceding and following the French Revolu- tion (1791) — as crucial a period for modern chemistry as for modern politics, though for vastly different reasons. Somewhat previous to the year 1770 the French scientist Lavoisier was attracted by the twin phenomena of combustion and calcination, owing, in the first instance, to a request to investigate means for lighting the streets of Paris. As a physi- cist (and physics at that time meant mainly astronomy, optics and mathematics — all three sciences requiring precision of measurement) it was natural that he should have paid much more than usual attention to the quantity of the substances re- acting, and that to this end he should have provided himself with a delicate balance. In 1772, in a private communication THE CHEMICAL HISTORY OF WATER 25 to the French Academic des Sciences, he reported that metals, phosphorus and sulphur gain in weight and absorb " air " when heated in the atmosphere, while by heating a metal oxide (litharge) with coal much " air " was generated, as well as the reduced metal. This report betrays a tendency to go to the opposite extreme of the usual failing, or, in other words, to neglect the qualitative side of chemical reactions, for he failed almost entirely to distinguish between the different kinds of "air". Let it be remarked, too, that increase in weight on calcination had been observed by Rey and Mayow more than a century previous to this, the latter being apparently well on the way to the correct explanation of the process when, at a somewhat early age, he died. Lavoisier, however, repeated the work of 1772 and produced a series of results which settled once and for all the problems of combustion, calcination, and respiration. These must be briefly summarized. In 1774 he heated tin in a closed vessel and found the weight to be exactly the same before and after the process ; but on opening the vessel air entered into it in an amount which showed that the deficit of air in the vessel was equal to an increase in weight which the tin itself was found to have undergone. During the same year Priestley told him of the isolation of " dephlogisticated air". Lavoisier then repeated the tin experiment with mercury, and from the oxide formed he reproduced the new gas according to Priestley's method ; in this way he realized that the essential part in these processes was .played by "dephlogisticated air " — it is unfortunate to have to say that he avoids any mention of either Priestley or Scheele's work on the discovery of that gas ! The next two years were occupied by proving that the combustion product of diamond and of wood charcoal was " fixed air," and that many " organic " bodies (alcohol, oils, fats, etc.) gave only fixed air and water by their combustion ; this, of course, showed such bodies to be made up only of carbon, hydrogen (and perhaps oxygen), but 26 A SHORT HISTORY OF CHEMISTRY the composition of water not being then known, this deduction was not made for some few years. In 1777 he showed that phosphorus leaves four-fifths of the volume of enclosed air in which it burns untouched, but completely consumes similarly enclosed dephlogisticated air ; that sulphuric acid consists of sulphurous acid (known to be formed when sulphur burns in air) and dephlogisticated air, by prolonged heating of quick- silver with sulphuric acid, when first the former and then the latter gas is evolved (this experiment, in separate parts, had been made previously by Priestley) ; and that nitric acid is similarly constituted (the more detailed investigation of the composition of nitric acid is due to Cavendish). With all these facts, he was in a position to enunciate his "oxidation theory" : Substances burn only in "pure air" which is used up in the pro- cess^ the weight of air used balancing the gain in weight of tJie substance. Tfie product of combustion is usually an acid, but metals give the metallic calces. A little later, concluding that his " pure air " was a constituent of all acids, he suggested its modern name, oxygen (1781). This later work consisted in investigating the combinations of metals with oxygen and the nature of the different " calces ". The only difficulty in the way of his theory was that no explanation was given of the reasons for the dissolution of metals in acids and the evolution of hydrogen at the same time. Cavendish's synthesis of water (1783) gave the clue to this, and so it may be said that by about 1785 Lavoisier's " oxidation theory " was complete, and in the course of the next two decades completely supplanted the topsy-turvy explanation furnished by the phlogistonists. CHAPTER III THE ULTIMATE CONSTITUTION OF MATTER § i. Ancient and Alchemical Yiews — In the sixth cen- tury B.C. Thales, Anaximenes and Heraclitus assumed for varying reasons that water, air, or fire respectively was the primary material out of which the universe was evolved. Such views were not of great individual influence, but Empedocles, about 440 B.C., gave utterance to the idea of four fundamental elements — earth, air, fire, and water — a view possibly derived in some degree from dimly-known Hindu and Chinese systems of thought. Some hundred years later Aristotle modified this theory by teaching that " matter " was the outward result of the combination of " properties " ; there were four essential " pro- perties"— heat, cold, damp, dryness — besides a number of secondary ones, all carried about by one original matter. Combinations of these properties, two by two, were the "elements" from which all matter was made; thus: — Properties. Element. Properties. Element. Heat + damp AIR Cold + damp WATER Heat + dryness FIRE Cold + dryness EARTH He further declared that another element of an immaterial or ethereal nature was necessary for a complete explanation of natural phenomena (this ethereal constituent was later called the " quinta essentia," and long after this was sought by the alchemists as the " purest " form of matter, and identified by them with their imaginary elixir). Aristotle's somewhat fanci- ful doctrine is noteworthy, because by the mutation of his 27 28 A SHORT HISTORY OF CHEMISTRY "properties" the observed transformations of natural bodies could be explained. Somewhat earlier (about 425 B.C.) Democritus had suggested that by repeated subdivision of matter a point would be reached when no further subdivision was possible. The body thus isolated — a " first beginning," or atom of matter — was the ground material of the universe, and, according to our philo- sopher, all such atoms were of the same nature and in continual motion, but differed in form and size. These two doctrines were co-ordinated and developed by succeeding philosophers, notably by Epicurus (345-274 E.G.), and an elaborate account of the latest phase of ancient theory is given by the Latin poet Lucretius in his work, " De Rerum Natura," published about 58 B.C. "The void, or aether, per- vades everywhere, while the matter is made up of a certain primal element and its aggregates. This element exists in the form of infinitely small, ever-vibrating first-beginnings or atoms, of finite shape, but giving rise by varied combinations to bodies of infinite shape, either solid (when the atoms are tightly packed) or liquid or gas, air or light (when they are not in such dense aggregates)." The term element possessed an indefinite meaning in the next period, and sometimes referred to the actual matter in a substance, sometimes to a property of that matter, but never to a simple substance! In general, the alchemical "element" meant something more related to properties than to matter itself — something which we can perhaps best depict by the word "principle". Thus Geber (eighth century) states (it is not clear upon what grounds) that all metals contain two such principles — sulphur and mercury, the latter imparting metallic properties, such as glance, ductility, etc., and the former readiness of decomposition, the different properties of metals depending on the varying amounts of these two principles, which, however, must not be confounded with the actual chemical substances of the same name, Quicksilver and sulphur, in the usual sense, THE ULTIMATE CONSTITUTION OF MATTER 29 were assumed to be bodies containing maximum amounts of the respective principles. Other Arabian authors held much the same view, but amongst the Christian nations the influence of the Aristotelian doctrine and of a mystical importance attached to the number three is noticeable. The third " prin- ciple," first assumed by Basil Valentine (fifteenth century), was " salt," the principle of resistance to fire. Some alchemists used different names for the principles ; thus Albertus Magnus calls them water, arsenic, and sulphur, and so it is hard to make any serious generalization on the subject. The iatro-chemists natur- ally paid less attention to the ultimate composition of substances, and this perhaps led to the loosely defined way in which the three principles are referred to by many of the later alchemists ; these were, however, always tacitly assumed, and Paracelsus (sixteenth century) asserts that organized as well as inert nature consists essentially of varying combinations of " sulphur, salt, and mercury". Finally Becher (seventeenth century) gave these alchemical elements a new series of names, as appears in the following summary : — ALCHEMICAL PRINCIPLES. Of Solidification Of Metallicity Of Changeability or Resistance or Durability. or Dross. to Fire. Geber . . Quicksilver Sulphur Basil Valentine . „ „ Salt Parace,-. - {$&££} Becher . . Mercurial earth Combustible earth Vitreous earth The lax nomenclature as well as the duplicity of not a few alchemists was scathingly criticized towards the close of the seventeenth century by Kunkel and by Boyle, who was the first chemist to say precisely what he meant by " element," giving at the same time a definition which has lasted : a substance which has not yet been decomposed into simpler ones (" Chemista Scepticus," 1661). While suggesting that the then so-called elements were not necessarily simple, he yet predicted a much 30 A SHORT HISTORY OF CHEMISTRY larger number of real elements than the Aristotelian four or the alchemistic three, although he doubted if the elements so obtainable by chemists would represent the absolutely ultimate origin of matter. § 2. The Evolution of Chemical Nomenclature — No further contribution of any permanent value to the problem took place for a century after Boyle's time, for, naturally, so long as people were in error with reference to the supposed phlogiston there was an inversion of opinion as to whether " calx " or " metal " was the real element. As soon as Lavoi- sier's theory of combustion was definitely accepted the way was open for a sweeping generalization of the host of chemical sub- stances then known. Lavoisier himself undertook the task (1787), adopting as the basis of his system Boyle's definition of an element. With a few modifications he used the nomen- clature introduced a little earlier (i 782) by Guyton de Morveau, one of the founders of and professor of chemistry in the " Ecole polytechnique " at Paris. This was as follows : — CHEMICAL SUBSTANCES. Elements. Compounds. (Five classes.) (Two classes.) (i) Heat, light, oxygen, nitrogen, hydrogen. (i) Binary (acids, bases), (ii) Acid-forming elements (sulphur, car- bon, etc.). (ii) Ternary (salts), (iii) Metals (we should say "heavy" metals, iron, copper, etc.). (iv) Earths (lime, magnesia, alumina, etc.). (v) Alkalies (only decomposed by Davy years later). Acids and bases, being regarded at that time as combinations of an element with oxygen, were termed binary compounds. Lavoisier's chief alteration had reference to the last two classes of " elements," of the simple nature of which he was doubtful ; indeed, two years later he felt the necessity of elimi- nating the alkalies entirely from the list of elements. We may THE ULTIMATE CONSTITUTION OF MATTER 31 as well complete the story of chemical nomenclature at this point ; as we shall shortly see, the discovery of the fundamental rules of chemical combination and the doctrine of ' ' atoms " in its modern form soon followed the adoption of Lavoisier's views. These in turn led to the investigation and accurate analysis of a great many inorganic materials, and in this field no more active and skilful worker existed than the great Swedish chemist Berzelius. His enlightened views and abundant experience fitted him for the work of extending and adapting Lavoisier's nomen- clature to include the additional facts known by 1811. In that year he published his first system of nomenclature, based upon his electro-chemical or " dualistic " theory of chemical union (see chap, iv., p. 50) : — CHEMICAL SUBSTANCES. Elements. Compounds. Electro-positive. Electro-negative. Electro-positive. Electro-negative. Metals. Metalloids Basic oxides. Acid oxides. (" non-metals "). v » ' Salts. He tried to extend the dualistic system and its nomenclature to organic compounds, but met with little success in that direc- tion. He also invented a simple method of chemical " short- hand," or abbreviation, which is practically that now in use, and so need not be detailed here. A certain amount of confusion resulted from the fact that Berzelius referred all his formulae to the " oxygen " standard, or, in other words, took a bivalent ele- ment as unit of combination, and, further, was not definite with reference to the distinction between equivalent and atomic weight. This led him to the use of " barred " symbols to repre- sent what he called " double atoms " in the case of compounds containing two monovalent atoms combined with oxygen ; thus he wrote HO and not H2O, and so on. This ambiguity may be the reason why his notation, now universally adopted, was at first received with a good deal of coolness, and, indeed, open 32 A SHORT HISTORY OF CHEMISTRY opposition, especially in conservative England. The only other modern notation emanated from Dalton, who assigned to the more common elements various geometrical symbols, and repre- sented their combinations by placing the appropriate symbols in juxtaposition. This method was naturally far too cumbrous to be permanent, though doubtless it was of value in the early struggles of the atomic theory, giving, as it must have done, a mental picture of the way in which the atoms united to form compound bodies. § 3. Discovery of Equivalent Combining Proportions — Given Boyle's definition of an element and Lavoisier's proof of what substances were elementary and what were compound, it is possible without reference to any further hypothesis to divide chemical substances into the different classes enumerated by Berzelius. This does not apply, of course, to the Berzelian notation, which, as far as its quantitative significance is con- cerned, is based upon the atomic hypothesis. It only remains now to discuss this important subject and its later development, for all modern work connected with Dalton's theory has so far served to amplify and not to contradict it. The establishment of the theory is really due to both English and Continental workers. No one has ever questioned that the genius and perception of Dalton led to his enunciation of the doctrine of atoms ; it was his idea, and was confirmed by his own experimental work. Nevertheless, when his views were published, it was seen that other and somewhat earlier work afforded strong confirmatory evidence in support thereof. For instance, J. B. Richter (1791-1800) showed that mixed solutions of two neutral salts invariably remained neutral, whether double decomposition took place or not ; he concluded that the two quantities x and y of two different bases X and Y which neutralized the same amount a of an acid A would each neutralize an amount b of another acid B, and conversely. He also measured the different amounts of metals precipitated from salt solutions by certain other metals, and gave to the THE ULTIMATE CONSTITUTION OF MATTER 33 ' whole process the name Stoichiometry — the measurement of the proportion by weight in which substances combine. Again, in 1808, shortly after Dalton had published his theory, Gay-Lussac published results on the volume relations of re- acting gases, showing that the volumes entering into combina- tion bore to each other and to the products (if gaseous) a simple numerical ratio. Thus he proved that 2 volumes of carbon monoxide and I volume of oxygen give 2 volumes of carbonic acid. I volume of. nitrogen and 3 volumes of hydrogen give 2 volumes of ammonia. He readily perceived in this a confirmation of Dalton's view, while, curiously enough, the latter worker, as we shall shortly see, was inclined to regard it as a stumbling-block. §4. Dalton's Atomic Theory — How, then, was Dalton led to the conception of his " atoms " ? It came about entirely independently of all this previous work, and, in a more distinc- tive way than many other famous advances in science connected with different names, was due to the man's own work and thought. He had been analysing olefiant gas (ethylene) and light carburetted hydrogen (methane) and found that, for a given amount of carbon, the latter contained exactly twice as much hydrogen as the former. Struck by the simple relation thus disclosed he proceeded to analyse carbonic oxide and carbonic acid gas, of course with precisely similar results. In this way the Law of Multiple Combining Proportions was dis- covered, and its truth was emphasised still further when he investigated the series of four nitrogen oxides and acids then known. What did this simple numerical rule imply? Some earlier researches by Dalton helped him towards an answer. In some work on the solubility of gases in water he had, like his con- temporary and colleague, Henry, noted how pressure increases the capacity of a gas to dissolve. It seemed as if the water was a mass of minute particles between which the gas particles, 3 34 A SHORT HISTORY OF CHEMISTRY which would be " rarer " and more volatile, could move to a certain extent, and then by increased pressure more of the gas particles would be forced into the interstices of the water- particles. Thus supplied with the rudimentary idea of an atom, it was easy to extend it. If the gases were an assemblage of such particles, in any one gas all the particles must be alike, and moreover any action in which the gas participated must be made up of the actions of the several particles. In other words, when two gases joined to form a third, the process was the result of the union of their constituent particles. It was obvious, too, that one particle of a substance might be joined to one, or to two, or to some other definite number of particles of another substance — thus explaining the rule of multiple pro- portions. So in 1807-8, the Atomic Theory was enunciated as follows in Dalton's " New System of Chemical Philosophy " : — (1) Every element consists of homogeneous atoms of constant weight. (2) Chemical compounds are formed by the union of different elementary atoms in the simplest numerical proportions. Dalton naturally proceeded to the determination of the re- lative atomic weights of the elements, assuming that these combined in the simplest possible atomic proportions, and taking hydrogen as the unit of his system. These results, which were not very accurate, expressed therefore the equivalent combining weight, and not the atomic weight (in the modern sense of the term). Dalton's theory differs from the old Greek views of atoms and from Boyle's "corpuscles," which were the ultimate par- ticles of matter and by mutual attraction and repulsion pro- duced chemical combination and decomposition, in that it demands that the atoms of each element are entirely distinct species of matter, and, as first enunciated, places a bar against the notion of an ultimate primary material. He succeeded in showing : — (a) How the elements may be made up of atoms ; THE ULTIMATE CONSTITUTION OF MATTER 35 (b) How these atoms may unite to form compounds ; (c] How to determine the relative combining weights of the atoms. § 5. Development of the Atomic Hypothesis — The conception of atoms was at once accepted by the leading chemists, but most of these (e.g. Davy, Gay-Lussac, Wollas- ton) perceived that the actual relative weights determined according to Dalton's principles were merely the combining weights, and that no light was thereby thrown on the relative weights of the atoms themselves. There was also the other difficulty arising out of Gay-Lussac's " Law of Volumes " ; ac- cording to his work on this subject, for instance, one volume of nitrogen and one volume of oxygen gave two volumes of nitric oxide, whilst obviously one atom of nitrogen and one atom of oxygen would give only one "atom" of nitric oxide. The difficulty of an " atom " of nitric oxide occupying twice the volume of the atom of either element was cleared up by the Italian chemist Avogadro in 1811. He assumed that : — (a) Under equal conditions of temperature and pressure, equal volumes of all gases contained equal mimbers of molecules ; (b) There were two sorts of ultimate particles, " mole- cules integrantes " (molecules) and " molecules elementaires " (atoms) ; (c) The ultimate particles of an element might be molecules composed of more than one atom. Returning to the previous point, viz. the difference between equivalent weight and atomic weight, we might fill a chapter with a description of the uncertainty and confusion which pre- vailed in the first half of last century with respect to these two terms. Some, like Davy or Gay-Lussac, held that the deter- mination of the relative weights of atoms themselves was impos- sible ; others, and of these Berzelius was foremost, adopted the opposite conclusion. Berzelius himself attacked the problem with amazing thoroughness, and in the course of ten years had made fairly reliable analyses of compounds of practically all the 36 A SHORT HISTORY OF CHEMISTRY known elements. From the equivalents so obtained he chose his atomic weights on the following system : — (a) With elements possessing volatile compounds he made use of Gay-Lussac's and Avogadro's volume-relations. Thus, starting from 2 volumes of hydrogen and i of oxygen giving 2 of water, he saw that in water 2 atoms of hydrogen were united to i of oxygen, and so obtained the true atomic weight of oxygen. (b) With other elements he worked on the ratio of metal to oxygen, and assumed that in general only i atom of the metal was present per molecule. In this way he came to regard proportions such as 2 : 3 or 2 : 5 as too complex, and therefore formulated the iron oxides, for instance, as FeO2 and FeO3, and not FeO and Fe2O, as at present ; so that what we now know to be dyad metals received double, and monad metals received quadruple their present atomic weights. (c) He always took oxygen for the basis of his calculations, and indeed, in his tabulated results, took 100 as the atomic weight of oxygen. (Later on it was thought better to refer all atomic weights to H = i as the standard, since hydrogen was the lightest element. In this way the atomic weight of oxygen becomes 15*88, and, since the majority of atomic weight deter- minations involve the ratio element : oxygen, it has latterly be- come the custom to call the atomic weight of the latter 1 6-00, and refer hydrogen (1-008) and all the other elements to this value.) This first atomic weight table of Berzelius was complete about 1817. We can only briefly summarize its subsequent career. In 1819 Mitscherlich brought out his " Law of Isomorphism," stating that the amounts of elements which replaced each other in isomorphous compounds were chemically equivalent and represented the relative weights of the replacing atoms, and about 1821 Dulong and Petit showed that in many cases the product of specific heat and atomic weight was a constant number. Both these rules were of assistance to Berzelius, though he attached but a minor importance to the second. THE ULTIMATE CONSTITUTION OF MATTER 37 His second atomic weight table (1826) was rendered neces- sary because he found reasons for halving many of the values he had previously selected. Analyses of the chromates showed that chromium trioxide was repre- sented by CrO3, so that the basic oxide must be Cr2O3. Hence ferric oxide was Fe2O3 and the " protoxide " FeO, and by isomorphism he deduced similar atomic weights for the allied metals. Next year, however, doubt was cast on his fundamental assumption that the weights of equal gaseous volumes of the elements were proportional to the atomic weights by the French chemist Dumas, who, by his vapour density measure- ments (cf. p. 179), obtained in some cases values which were multiples or sub-multiples of the Berzelian numbers. This and the slender basis of Berzelius' assumptions about the atomic composition of compounds led most people to despair of ever finding the relative masses of the actual atoms, and a strong reaction set in against his interpretation of the atomic doctrine. Between 1830-50 further confusion arose. Gmelin, a Ger- man worker, insisted on taking the simplest empirical com- bining ratios as the equivalents and neglecting atomic weights altogether, thus halving nearly all the Berzelian values. A few years later Gerhardt noted that on this hypothesis more than one equivalent of water or carbonic acid always resulted when one equivalent of an organic compound was burnt, so he decided for the old numbers, except that he regarded all metallic oxides as composed of two atoms of metal and one of oxygen. All three systems were used concurrently by different workers, and a few, not content with the muddle, increased it by calling the equivalent of oxygen 8 but that of carbon 1 2 \ Atomic Weights Berzelius Berzelius Final (o = 16). (1818). (1826). Gmelin. Gerhardt. Value. Hydrogen i i i i i Oxygen 16 16 8 16 16 Carbon 12 12 6 12 12 Iron . . . rog 54-5 27 27 56 Sodium . . 93 46-5 23 23 23 38 A SHORT HISTORY OF CHEMISTRY Fortunately the French chemist Laurent (1843) partially cleared up the confusion by giving precise definitions to the chief terms involved, namely, equivalents, the mutually replace- able quantities of similar and similarly combined elements (consequently not always the same for each element) ; atoms, the smallest particles participating in reactions ; molecules, the smallest particles capable of free existence ; molecular weight, the weight of a chemical substance occupying the same volume as a molecule of hydrogen. And Cannizzaro in 1858 helped still further by summarizing the methods of atomic weight determination according to reliability as follows : — (a) Vapour-density determination of compounds as well as elements. (*) Specific heat determinations j ^ due reswvation (c) Isomorphism § 6. The Periodic System — The inquiry into the manner of union between elements to form compounds has always been closely accompanied by observation of the similarity or dis- similarity of the various elementary bodies. Theories of the mutual relations of the elements have, since the establishment of the atomic theory, developed along two lines : — (a) Discussion of the ultimate composition of the atoms, a problem which we survey a little later (p. 41). (b) Investigation of regularities in the chemical behaviour of the elements. Until Cannizzaro 's systematization of the atomic weight values, only fragmentary evidence of any connexion between properties and atomic weights was available, but instances of apparent rela- tions of this kind were very soon noticed here and there, especially by Dobereiner of Jena, who in 1829 showed that some series of chemically analogous elements could be arranged in " triads " whose atomic weights were in approximately arithmetical pro- gression, e.g. lithium, sodium, potassium ; calcium, strontium, barium ; chlorine, bromine, iodine. It was also seen that other THE ULTIMATE CONSTITUTION OF MATTER 39 triads of very closely related elements possessed almost identical atomic weights. At about this time the " homologous series " into which so many organic compounds fall were being outlined, and Dumas sought to show that the atoms themselves possibly formed in some way a series based on somewhat similar lines; other arith- metical regularities were pointed out by Odling in 1864. The idea, though ingenious, was not supported to any great extent by facts. There are no other views sufficiently important to be recorded until after the atomic weight confusion was removed in 1858, but almost within a decade of this advance the periodic classi- fication of the elements was accomplished. In its simplest form this, which is the basis of all modern inorganic theory, was stated by Newlands in 1864 ; he showed that by tabulating the known elements according to increasing atomic weights " each eighth element, starting from a given one, was a sort of repetition of the first " (the " Law of Octaves "), but little serious attention was paid to his discovery in England, and the honour of evolv- ing the complete periodic system was divided five years later between Lothar Meyer of Germany and Mendelejew of Russia. The former showed that physical properties (atomic volumes) and chemical properties (valency) varied periodically in each group of eight elements and stated that the properties of the chemical elements are periodic functions of their atomic weights. The latter drew up a complete table of all the elements known at the time, arranged according to the *' periodic law " and attracted much notice by the confidence with which he used his newly found " law " to correct the atomic weights of some elements and to predict in marvellous detail the characteristics of three elements at that time unknown. Both corrections and predictions have been justified, the former in the cases of beryllium, indium, and uranium, the latter by the discovery of scandium, gallium, and germanium. While the usefulness and general correctness of the system 40 A SHORT HISTORY OF CHEMISTRY have been admitted on all hands, difficulties have from time to time appeared and some have not yet been removed. The chief obstacles which have been encountered are : — (a) The groups pass from a strongly electro-positive element (e.g. lithium) through gradually decreasing basic elements and finally reach a strongly electro-negative element (fluorine), after which, without any gradual transition, the next element is again highly electro-positive. (b) The analogous elements of approximately equal atomic weights (such as iron, cobalt, nickel) do not find any suitable place in the table. (c) Some elements of widely varying chemical behaviour are brought into close juxtaposition ; such are the alkali metals, silver, copper, and gold. (d) Some closely related elements are separated in the table ; such are silver and thallium, or barium and lead. (e) The position of argon and potassium and of tellurium and iodine according to their properties is the opposite of that demanded by their atomic weights. These objections have been partly met as follows : — (a) The " new " non-valent gases of the atmosphere occupy, from their atomic weights, positions intermediate between the extreme electro-positive and -negative elements, and Ramsay suggested that they form the transition elements previously lacking. It will be noticed incidentally, that the original " Law of Octaves " has become a " Law of Ninths ". (c) and (d] It is urged that the resemblances or dissimilarities, as the case may be, of the various elements concerned are on the whole best satisfied by their present positions in the table. (e) Many are the re-determinations of the atomic weights of tellurium and iodine which have been carried out in the hope of reversing their order. But the consensus of the results tends to show that the accepted values are correct and that this, to- gether with the argon-potassium anomaly, must be left at present unexplained. THE ULTIMATE CONSTITUTION OF MATTER 41 Various difficulties have been at one time or another partly removed by attempts to re-cast the system ; among such efforts may be mentioned those of Johnstone Stoney (1888), Walker (1891), and Staigmiiller (1902). In concluding this section, it must be emphasized that Mendelejew's designation of the periodic system as a "law" is somewhat of an exaggeration. The real law which underlies the system has not been discovered, although it may be surmised from the results obtained in the past few years, that the essential principle concerned depends on the constitution of the atoms themselves, upon which question the electronic theory of matter will no doubt in the course of its future development throw considerable light. § 7. Is all Matter derived from one ultimate Funda- mental Material ? — When Dalton's atomic weight numbers were tabulated with reference to that of hydrogen (the lightest) as unity, the values for the few elements then determined were nearly all very approximately whole numbers. There has al- ways been an instinctive desire on the part of philosophers to make simple generalizations wherever possible ; it was natural to think that the heavier atoms were made up in some way of a definite number of " condensed " hydrogen atoms. The suggestion is connected with the name of Prout and first ap- peared in 1815. For a long while it was regarded sympathetic- ally, then gradually the accumulation of evidence against it changed the opinion of chemists, and for year.s now it has been the custom to speak rather lightly of " Prout's hypothesis ". It is pointed out that, firstly, the values on which it was based (Dalton's and T. Thomson's) were hopelessly inaccurate ; that, secondly, several workers with a strong prepossession in its favour set out to gather evidence for its support and returned convinced of its untenability ; that, thirdly, other workers have tried to invent modified forms of the hypothesis and have usually conspicuously failed. And yet, in spite of the cool reception which Prout's views meet with at the present time, 42 A SHORT HISTORY OF CHEMISTRY communications are intermittently appearing in the scientific journals from observers who think they have found a means of calculating the atomic weights of the elements or of indi- cating how the latter have been " evolved " from a primordial material. The accurate determination of chemical equivalents by Ber- zelius and others soon compelled the upholders of the original hypothesis to shift their ground; and in succession the half and the quarter of an atom of hydrogen were put forward as the " unit " of matter. This repeated subdivision of the " unit " of course destroyed the original form of the idea. Dumas, Marignac, and Stas were three noted stoichiometric investigators, each of whom started to collect evidence to bear upon Prout's view, and all concluded that there was no such simple relation subsisting between the elements. Stas, indeed, executed a series of researches which were for all time a model of manipulation and skill : true, of late years sources of error have here and there been detected in them, but every such source of error known to Stas at the period of his work (1840- 65) was eliminated with perfect care. Dumas, whose work was a little prior to that of Stas, and who suggested that the elements formed " homologous series " among themselves similar to the series of hydrocarbons, etc., discovered in organic chemistry, and also Pettenkofer (1850) devised mathematical formulae whereby to deduce the atomic weights of the heavier from those of the lighter elements, but such equations were scarcely approximately exact. A few years subsequently there comes a division in the speculations as to the mutual relations of the elements. One line of thought was concerned solely with the resemblances in properties of the various elements and sought to find a working hypothesis by which to be guided in the general problems of chemistry ; this helped to lead to the evolution of the " periodic classification of the elements ". The other, the more speculative and philosophical line of thought, deals with THE ULTIMATE CONSTITUTION OF MATTER 43 the " genesis of matter " and the constitution of the elements themselves. It may be said that this problem, too, has been approached from two sides : spectroscopic and electrical. For a number of years from about 1865 onwards, Sir W. Lockyer made a detailed study of the spectra of the different stars and found that the hottest stars contained chiefly hydro- gen and other gases (some then unknown terrestrially), the less hot stars contained the metals with which we are familiar on earth, and the coolest were carbonaceous stars. Again Sir W. Crookes, investigating the "rare earths" obtained from " yttria " (originally supposed to be the oxide of one element, yttrium), split these up into eight different fractions which were in almost every respect chemically alike, but gave different phosphorescent spectra. The former research seems to show that in star-formation a process of building-up of the heavier elements from hydrogen — or something lighter — is going on ; the latter that there exist elements so closely related as to be more like "varieties" than distinct "species" of elementary matter. On this basis Crookes in 1886 suggested that the old doctrine of the unity of matter might be true and that all the elements were condensation products of a primary material, "protyle". The fact that Kayser and Runge, and others, have recently shown mathematical or " harmonic " relations to exist between the wave-lengths of similar groups of lines in different elementary "spectra" is held to be further evi- dence of similarity in the different atomic structures. On the other hand, Crookes opened up a new line of attack about 1880 by studying the action of electric discharges in vacuum tubes. The "cathode rays," which he was thus the first to study, have since been characterized by Sir J. J. Thom- son and others as streams of rapidly-moving matter, as particles whose mass was about the thousandth part of that of a hydro- gen atom, and, finally, as particles or atoms of electricity, which has thus itself come to be regarded as material, or rather, we 44 A SrtORt HISTORY OF CHEMISTRY recognize now that the basis of matter is electrical. Dr. Johnstone Stoney named these atoms " electrons " — a name which has lately become very familiar. Now, since in electrolysis, etc., a definite amount of elec- tricity is always connected with the liberation of an atom of any element, and also since the " radio-active " metals break down ultimately into these electrons, it has appeared natural to regard the atoms of electricity as the basis of the constitution of the elements, and here we come to the most modern phase of that curious ever-present speculation as to a " primary form of matter ". Most people at present regard the electron as tJie funda- mental "stuff" of which "the world is spun," but views differ as to how the different atoms are made from the elec- trons, and of course there is absolutely no experimental evid- ence to show. From time to time, suggestions are offered ; in 1908 Jessup showed how by addition of groups of electrons to four " protons " or fundamental elements, all the elements in the periodic table could be accounted for, either by building up or by "degradation " of atoms already so formed ; in 1909 Egerton put forward the most accurate method of "calcula- tion " of atomic weights yet devised, based on the fundamental assumption of electrons and accurate in most cases to the second decimal place when compared' with the best experi- mental values (his work only applied, however, to the twenty- eight lightest elements, and has been disputed, moreover, by Moir on the ground that the agreements found are due to mathematical necessity). Chemists have, therefore, made fair progress of late years towards deciding the vexed question of the " unity of matter," but there is still much to be done. The outstanding points of their work in this direction have now been briefly mentioned, and we must leave the story as it is — unfinished. CHAPTER IV INORGANIC COMPOUNDS AND THE LAWS OF CHEMICAL COMBINATION § i. Chemical Affinity and the Manner of Chemical Combination — The German alchemist, Albertus Magnus, seems to have first suggested the name " affinity " to express the force which leads certain chemical bodies to react with certain others. Ideas as to the nature of the force were in those times prolific and fanciful ; Glauber believed the different sub- stances to " love " or " hate " each other, others thought that combination was effected by hooks or pointed prongs on the ultimate particles of matter. Some thought that similar bodies, others that dissimilar bodies, exerted most mutual attraction. The first scientific treatment of the problem occurred when Geoffroy in 1718 tried to construct " affinity-tables," consisting of lists of substances (acids and bases), in order of increasing or decreasing affinity with respect to a fixed base or acid. How- ever, in the phlogistic era little progress was made, because the most important factor — mass — was left out of consideration altogether. In 1775 Bergmann practically stated that mass made no difference at all, for he said that if, in the case of a substance YZ, the part Y had more affinity for another part X than for Z, then, if X be present, it would become entirely united to Y at the expense of Z, by virtue of its greater affinity. On the other hand, Wenzel in 1777 discovered the "law of mass- action " (which did not reappear till nearly a century later) by 45 46 A SHORT HISTORY OF CHEMISTRY urging that the " amount of chemical action is proportional to the concentration of the acting substance ". About 1 80 1, Count Berthollet declared that the predominant factor in chemical union was the relative masses of the sub- stances concerned and not their affinity ; this was of course the diametrical opposite of Bergmann's views, and was based on his conception (and men like BurTon, Newton, and other philo- sophers, had held the same idea) that the force determining chemical action was identical with gravity. He, therefore, sup- posed that this, like gravity, was dependent on the masses of the reacting compounds, but pushed his views too far by imagining that any (and not definitely " equivalent ") masses of two sub- stances could unite to form a third. In the ensuing six years Proust contested his view, and proved by experimental work on the basic carbonates of copper, the two oxides of tin, the two sulphides of iron, and other compounds, that Berthollet was wrong, that combination only took place in constant unvarying proportions, and that if two elements united to form more than one compound, the composition varied by leaps from one pro- portion to another, and never gradually passed from one to the other. The excellence of Proust's experimental work forced Berthollet to admit he was mistaken, and to modify his theory accordingly. In its modified form, of course, it was correct, for, as has been increasingly recognized, the mass of the reacting substances present plays a very important part in determining the course of a reaction. Soon after this time the close connexion between electricity and chemical affinity began to be pointed out by Davy, Berze- lius, and others, but as this concerns the structure of inorganic bodies rather than the point we are now studying we will leave it for a moment. During the first half of last century the results of numerous researches tended to support the essential or modified part of Berthollet's theory. For example, H. Rose made an extended examination of the part played by water in various actions INORGANIC COMPOUNDS 47 where, given suitable conditions, it can displace relatively strong acids (1842) ; he showed how in some cases (iron, mercury, etc.) basic salts are formed in presence of excess of water, while in others (alkaline sulphides) complete hydrolysis may occur. Somewhat later he discussed the influence of the varying pro- portions of the reacting compounds in cases of " double decom- position," and in 1855 Gladstone published important results dealing with the same class of reactions. Meanwhile, in 1850, Wilhelmy devised a formula to express the rate of " inversion " or hydrolysis of cane sugar which is essentially an enunciation of the modem form of the " law of mass action ". Further data towards this end were provided by the elaborate work of Berthelot and Pean de St. Gilles from 1 86 1 to 1863 on esterification ; they showed that, starting with equimolecular amounts of alcohol and acid, or of the corre- sponding ester and water, the same mixture of alcohol, acid, ester, and water will finally be reached, and that the final com- position of this mixture can be altered according to simple rules by increasing the acting mass of any of the constituents. On the other hand, thermo-chemical evidence which, again, helped to support the law of mass-action, was given by Julius Thomsen at varying times from 1854 to 1868. The most complete state- ment of the matter is always associated with the names of two Norwegian investigators, Guldberg and Waage. Supported by the facts which have just been summarized, and basing their arguments on Berthollet's proposition that " chemical equili- brium depends not only upon the affinity, but also essentially upon the relative masses of the reacting substances " (Nernst, " Theoretical Chemistry "), they affirmed that in all chemical actions the amount of action is proportional to the acting mass. Since we are merely treating the subject historically, it is im- possible to give the details of their argument, but we may repro- duce the familiar equation which represents the velocity V with which a given reaction will proceed : — 48 A SHORT HISTORY OF CHEMISTRY If substances of concentration clczc3 . . . are reacting to form new substances of concentration cVV*3 • • • where k, kl are numerical constants ; thus when equilibrium is attained, The treatise " fitudes sur les affinites chimiques" (1867) in which these results appeared remained comparatively unnoticed for some time, and indeed the generalization was subsequently made by other chemists, but in its most extended form it was developed, as we have said, by Guldberg and Waage. Van't Hoff (1877) and Horstmann (1869-77) succeeded in making approximately the same generalization in perhaps a more strictly logical or deductive manner from thermo-dynamical and mathematical considerations. There have been a number of studies published on the sub- jects of affinity and mass-action since the law was definitely stated in 1867 ; these are dealt with in Chapter x. It will be seen that the terms chemical statics and dynamics are by no means fanciful, for nowadays the problem of chemical affinity has been reduced, so to speak, to mathematical equations and numerical constants, and by such rigid means as these a knowledge of how the forces producing chemical charge act is being rapidly gained, but when it is asked what are these forces and why do they so act, we cannot tell. Having now outlined the work done on the general question of the rules of chemical reaction and formation or decomposition of compounds, we turn to the other aspect of the problem, viz. how are the various atoms joined, each to the other, in chemical compounds ? It will be convenient to restrict ourselves for the time being to inorganic compounds, for the theories of the structure of organic substances are in a far more advanced state than those of the former. § 2. The Structure of Inorganic Compounds — The purpose of this book prevents us again from dealing with the oldest views of structure, and we must confine ourselves to the INORGANIC COMPOUNDS 49 more modern facts and theories, which are certainly no less interesting.1 As chemists, however, we have to pay attention to present facts rather than past fancies or future chances. The facts upon which the structure of compounds depends are primarily the " laws " of constant and multiple combining proportions. We will call to mind then, how the former was definitely proved by Proust in 1801-7 (P- 4^)> and the latter also foreshadowed in Proust's work and definitely established by Dalton about 1808 (p. 33). With the united help of these laws and of Dalton's atomic theory, it seemed so easy to most chemists in the early decades of last century to devise formulae for all manner of compounds. And so it was, indeed, very easy ; but whether the formula bore any relation to the chemical behaviour of the compound in question was often quite another matter, and in not a few cases the older formulae absolutely fail to express the facts at all. In short, the problem of the structure of inorganic compounds was for a long while thought to be much more simple than it really is. The view that there was a mutual connexion between heat, electricity, and chemical force came to the front about 1800. Twenty years previously, Galvani had noticed the action of an electric current on the frog, and Volta had extended the know- ledge of electricity considerably, had devised his " Pile," and had suggested that friction of two dissimilar bodies was sufficient to endow them with electricity of opposite polarity. In 1807, Davy elaborated this view by holding that the smallest particles of substances (atoms) become oppositely electrified upon con- 1 There is a curious attraction about the old fanciful notions of many of the alchemists and phlogistic chemists which seems to make the story of their work much more interesting to read than that of later and present- day chemists ; perhaps the underlying cause is the same as that which makes a novel appeal to most people more than a history book, or, judging from current magazines, which renders the possibilities of "radium" or "electrons" more attractive to the "lay mind" than, shall we say, the constitution of quinine or the law of mass-action, 4 So A SHORT HISTORY OF CHEMISTRY tact (the intensity of electrification rising with increase of temperature), and that chemical combination results from neutralization of the opposing potentials. The sign of the potential of the combining elements could be experimentally determined, electro- positive elements being isolated upon elec- trolysis at the negative pole, and vice versa. In 1812, and more fully in 1819, Berzelius published the dualistic theory of chemical combination, which resembled Davy's in some fundamental points, but differed in that it was more systematically developed. He assumed that every atom possesses both + ve and — ve electricity, but in varying amounts. Thus some elements were positive, others negative, most were positive with respect to some, and negative with reference to other elements ; oxygen only was never positive to any element, and so was held to be purely electro-negative, and for this and other reasons was adopted by Berzelius as his standard or starting- point. The elements by combination furnished new bodies in which again an excess of one or other kind of electricity was present. Thus basic oxides came from the union of oxygen and strongly electro-positive elements (metals), and acid oxides from oxygen and the metalloids. This tended to confirm Lavoisier's view (p. 26), that all acids contain oxygen. Salts, and furthermore mixed salts and hydrated salts, were regarded as the product of union of the already compound bases and acids, an excess of one or other kind of electricity being always left over, but in less pronounced quantity than with simpler substances. This important theory served well to point out the constitution of the most obvious classes of inorganic compounds, viz. bases, acids, and salts. Berzelius, however, tried to push it further and attempted to systematize the organic compounds then known on the same basis. Until about 1840 his efforts met with complete approval, and the dualistic theory held practically universal sway. Soon afterwards it began to de- cline, chiefly through the influence of the following facts : — (i) In 1834 Dumas discovered the phenomena of "substitu- INORGANIC COMPOUNDS 51 tion " in organic chemistry, by which a strongly negative element (chlorine) replaced electro-positive hydrogen. (2) In 1839 Daniell showed that in the course of electrolysis the same amount of electricity will set free a definite amount of hydrogen on being led successively through water and a solution of sodium sulphate, but also, in the latter case, will liberate an equivalent of sodium hydrate, thus doing double as much work in the second as in the first instance, according to Berzelius' theory. (3) The dualistic hypothesis did not precisely explain why certain acids not containing oxygen (notably HC1) were as strong or stronger than many oxygen acids, containing the most electro-negative element of all. Many objections to the dualistic theory therefore arose about 1845-50, and, as usual, the reaction carried opinion to the other extreme, and it was sought to regard inorganic com- pounds as simply composed of the different "units" of atoms, in a similar manner to the way in which the structure of organic substances was beginning to be regarded at that time. The French chemists, especially Dumas and Wurtz, took the most prominent part in developing the "unitary," as opposed to the dualistic, idea. § 3. Valency — This word is synonymous with the terms " replaceable value," " atomicity," " saturation-capacity," and, like some other terms occurring at different periods of chemical history, it has tended to become somewhat of a< nuisance and to enforce conceptions entirely beyond its real simple meaning. It is a name for the " combining worth " of an element, ex- presses the number of equivalents of a " univalent " element with which the element in question can unite, and, as E. Meyer has said, is really nothing more than an expression of the laws of definite and multiple combining proportions. In 1834 Dumas showed in connexion with his substitution researches that one " atom " of chlorine replaced one atom of hydrogen, but that the latter was replaced by only a " half atom " 52 A SHORT HISTORY OF CHEMISTRY «^£oxygen. A little later Liebig noted that an antimony atom canbf mbine with three atoms of hydrogen, whereas the potas- siunf atom is equivalent to only one, and he also developed the knowledge of polybasic acids, showing that some acids contain only one and others (e.g. citric acid) more than one replace- able hydrogen atom. This brings out the idea of the equivalent as distinct from atom or molecule, and in 1843 Laurent gave definite expression to the term, and stated that elements could possess varying equivalents under varying conditions. The idea of a constant combining worth for each element was, however, very popular in those days, and Wurtz, for ex- ample, formulated numbers of inorganic compounds on the hypothesis that the elemental valencies were always fixed. Such formulae, which quite failed to represent the chemical behaviour, and were simply strings of letters, such as HOOOC1 for chloric and HOOOOC1 for perchloric acid (to give only one instance), prevailed in " text-books " for many years, and have not abso- lutely died out even at the present day. Kolbe wrote in favour of a "maximum valency " of each element in 1854 — indicating the existence of possible cases where all the " valencies " were not utilized. At about the same time papers were being pub- lished on the subject in England by Williamson and by Odling. Williamson's work was more concerned with the constitution of organic compounds (cf. chap, vi.), while Odling discussed the different combining powers of iron and tin, as shown in their varying oxides, and introduced, by the way, the term " replace- able value ". His adhesion to the " type " theory of organic com- pounds, by means of which he tried to classify inorganic acids, presumably prevented him from arriving at such conclusions as those deduced by another English chemist, Frankland. It is to the latter, indeed, that the clearest ideas about valency at this period are due. This work dates from about 1853 onwards, and his views were generally accepted by the year 1860. He noted how nitrogen, phosphorus, antimony, and arsenic behaved sometimes as tervalent and sometimes quinquevalent, and was, INORGANIC COMPOUNDS 53 therefore, led to regard them as analogous ; for similar reasons he classed carbon, silicon, titanium, and zirconium togethei>e< He did more than any of the contemporary workers forgive a definite meaning to "valency" or " saturation-capacity," as he called it : he showed how circumstances influenced the combining capacity of the elements, so that an element which under given conditions evinced no tendency to behave otherwise than, say, tervalent might, in other cases possess anbtb^r valency. He argued that such substances would p«sess * a maximum " saturation-capacity," but that all its possible " valen- cies " would not invariably come into action. This method of classifying elements according to similar combining power was, of course, a step in the direction of the " periodic classification," which we have already discussed (p. 38). On the Continent, on the other hand, events moved some- what differently. Gerhardt put forward views similar to Frank- land's as early as 1856, but in 1860 Kekule, arguing from the " organic "point of view, declared for the principle of constant valency. Blomstrand, Kolbe, and others debated the point during the next five years, the result being the confirmation of Frankland's theory. Erlenmeyer, about 1863, made an im- portant statement, which was in the main the same as Frank- land's, but extended the latter by the conception that valency was due to the number of " points of affinity " possessed by each element. This has had a somewhat unfortunate sequel, for it is probably the innocent cause of the excessive emphasis which has so often been laid on the modern " structure-for- mulae," in which union is depicted by dashes. It is interesting to speculate how many people have consciously or uncon- sciously conceived the dashes as an image of the real mode of union of atoms. The signs mean nothing except that one atom is "united" with the next — how precisely no one knows. The point as to whether all the affinities of a polyvalent ele- ment are of equal worth has been pretty thoroughly discussed since the modern idea of valency took firm hold. The experi- 54 A SHORT HISTORY OF CHEMISTRY mental investigation has centred round derivatives of carbon (Roscoe and Schorlemmer, Henry (1888)), sulphur (Kruger, Klinger), and nitrogen (hydroxylamine derivatives, etc., by Lossen, Beckmann). This simple conception of valency, however, is not enough to explain many facts which have come to light of late years. These new points generally concern the structure of organic bodies, but for the sake of compactness will be presented here. The reactions of substances written asR.CH = CH.CH = CH.R1 are quite anomalous according to this formula ; on reduction or ad- dition of halogen they yield R. CHX. CH = CH. CHX. R1 exclusively, and not R . CHX . CHX . CH = CH . R1. In 1899 Thiele suggested that the affinities of elements were not always completely utilized, that in "unsaturated " compounds, com- pounds possessing " residual affinity," the carbon must be repre- sented as possessing " partial valencies," and that a better method of graphically representing them was R.CH = CH— CH = CH.R1. Assuming that the central " partial valencies " saturated each other he arrived at the formula R.CH = CH— CH = CH.RWR.CHX.CH = CH.CHX.R1. Again, complex salts of various metals are known which cannot be readily accounted for by the simple valence theory. Werner has advanced the view that such compounds (cobaltam- mines, cobalticyanides, etc. etc.) must be represented by a new method. Taking a concrete example, the following cobaltam- mine chlorides are known, the chlorine atoms outside the bracket being the only ones which become ionized in solution : [Co(NH3)6]Cl3, [Co(NH3)5Cl]Cl2, [CoCl2(NH3)JCl, and, finally, non-ionized bodies, such as [Co(NH3)3(NO2)3]. So far, as Blomstrand and Jorgensen showed long ago, there is no need to go beyond ordinary structure formulae, but some com- INORGANIC COMPOUNDS 55 pounds of the type [Co(NH3)4R.2]X each exist in two different forms, of characteristic colour. Werner attributes this to a new kind of stereoisomerism of the group within the square brackets thus : — R I NH3 NH,— CO— NH, NH3 and NH3 NH3 NH3— CO— NH3 R This mode of union he calls "co-ordination," to distinguish it from the usual union, expressed in terms of ordinary " valency ". Jorgensen, however, disputes the method of representation en- tirely, and since doubt also exists as to the correctness of some of the alleged observed facts, the matter must be left at this point.1 The whole subject of valency is thus still very unsettled ; it seems of late years as though the solution of the problem will ultimately be upon an electrical or electronic basis. In 1904 Abegg put forward the view that each element is potentially octovalent, the eight valencies being made up of positive and negative ("normal" and " contra ") valencies, as follows : — Periodic Table Group. Normal Contra + i - 7 II. + 2 - 6 III. + 3 - 5 IV. V. VI. VII. + 4 - 4 '-3 + 5 - 2 + 6 - i + 7 The extent to which the contra-valencies come into play depends partly on the nature of the atom itself, partly on the circumstances of its combination. This hypothesis is more or less a precursor of the purely electronic view. 1 Other views, involving less profound modification of existing ideas on valency, have been recently put forward by Friend (1908), Sir William Ramsay (1908), and Miss Baker (1909), in order to explain the structure of the metallammino derivatives, 56 A SHORT HISTORY OF CHEMISTRY In 1907 Sir J. J. Thomson suggested that elemental valency depends on the transference of electrons to or from the element atoms by the action of other element atoms, so that the " valency lines " really portray tubes of electric force towards or away from the atom. This view is being extended to the structure of organic compounds, and it is evident that it marks an advance upon the older theories, since it is a step in the direction of a hypothesis which may eventually present an explanation of all the varied problems of chemical structure and unite them into one simple theory. At present it appears difficult to get enough experimental evidence upon which to base an universal electronic theory of chemical composition. § 4. Electro-chemical Theories— It will be best to give at this point a collected account of the various hypotheses developed during the last hundred years with reference to electro-chemical decomposition. The general electrical theories of Davy (1807) and Berzelius (1812-40) have already received attention (pp. 49, 50), but the more particular explanation of the phenomena of electrolysis remains to be dealt with. The theory which found its way into text-books for many years was that of Grotthus (1805), according to which the electrolyte molecules, previously indiscriminately distributed through the solution, arranged themselves in " chains " through the liquid under the influence of the electric current, the par- ticles adjacent to the electrodes then separating, thus : — Current In 1854 Clausius applied the kinetic theory (which he had recently developed in the case of gases) to electrolysis. He assumed that the electrolyte molecules were in constant motion in the solution (a view previously expressed in more general INORGANIC COMPOUNDS 57 terms by Williamson in his work on the ethers ; cf. p. 84), and that consequently they were momentarily split up into their ions (to use the convenient modern term). Under ordinary circum- stances recombination took place at once, but in presence of a current the ions were separated at the electrodes, a mutual interchange of component parts ensuing between the dissolved molecules between the electrodes. The objection to both theories is that each presupposes a certain minimum electric force to be necessary for electrolysis, whereas the smallest current will effect electrolytic decomposition. The next great advance was the "ionic theory " of electro- lysis, established by Arrhenius in 1887, and foreshadowed as early as 1833 by Faraday. The latter scientist outlined the two chief " laws " of electrolysis (the amount of chemical action is proportional to the amount of electricity, and chemic- ally equivalent quantities of all ions are set free by the same quantity of current), introduced the terms "ion," "anion," "cation," and was convinced that "the power which governs electro-chemical decomposition and ordinary chemical attrac- tions is the same," and that the force acting upon the ions was "either superadded to or giving direction to the ordinary chemical affinity ". Arrhenius supposed that all electrolytes (according as they are "good" or "bad" conductors) are more or less dissociated in solution into ions carrying charges of "positive" or "nega- tive " electricity in proportion to their " valency ". The electric current simply acts as a directing force, causing the ions to migrate to either electrode and then to deposit their electric charges, after which they reappear as the usual chemical elements or groups, and may be then set free as such, or undergo further chemical decomposition with the electrode or the solution. This view found great support from other physico- chemical evidence, notably when Ostwald showed, by widely extended instances, that the electrical conductivity or affinity coefficient of acids and bases gave exactly the same order of 58 A SHORT HISTORY OF CHEMISTRY strength as that determined by a variety of physical and chemical methods (cf. p. 177). Another modern theory of electrolysis, the " hydrate " theory, must also be mentioned, but this is not apparently destined to have a great influence on chemical theory. The latest advances deal with the extension of the ionic theory, owing to the conception of the materialistic nature of electricity. When " negative " electricity was first shown to be material, it was naturally anticipated that there would be a corresponding " positive " electricity as well, but later work points to the conclusion that there is only one kind of elec- tricity— " negative electricity," or, using modern terminology, electrons. Consequently a certain amount of readjustment of the theories of electrolysis has become necessary, and this has lately been effected, notably by Ramsay (Presidential Addresses to the Chemical Society, 1908-9). It is suggested that the elementary atoms are combined with electrons in two ways — with "active "and with " latent" electrons. The number of latent electrons depends on the maximum valency of the ele- ment and the particular valency displayed in a given instance, while the active electrons are the cause of the displayed valency. Suggestions of a somewhat similar kind have also been made recently by Kauffmann, Stark and other chemists. Stark's view of the process involves the assumption that neutral water molecules are added to the ions, and thus accounts for the phenomena of hydration of the ions. CHAPTER V NOTES ON THE HISTORY OF THE ELEMENTS AND THEIR CHIEF COMPOUNDS HAVING discussed the general development of our views relating to the nature of elements and the manner of their chemical combination, we must devote a few pages to a description of the chief inorganic substances. In some cases there are in- teresting points connected with the discovery of an element or the production of a new compound, but as a rule the discovery of a particular substance is of very minor importance when com- pared with the principles governing the work in question or with the systematization of a class of compounds or of chemical reactions. We shall accordingly pay greater attention to the latter two lines of research, giving at the same time incidental prominence to the history of individual substances. The con- fusion, prior to about 1790, between elements and compounds— has been previously mentioned, so that it will be readily under- stood that although numerous inorganic or mineral substances were known long before that date, their systematic history only commences with Lavoisier, who classified mineral bodies into acidic and basic oxides, salts and elements. We will review them in this order, adding further sections upon the develop- ment of mineralogy, and the comparatively recent advances in radio-activity and the knowledge of the metals of the "rare earths ". § i. Acidic Oxides — When Lavoisier overthrew the phlo- giston theory he established in its place a system in which 59 60 A SHORT HISTORY OF CHEMISTRY oxygen played much the same part as the hypothetical " phlo- giston " in the preceding era — oxygen was the central point of his chemical system, since it united with every element known to him. Referring to his system of nomenclature (p. 30), we see that he called the compounds of the metals with oxygen, oxides or bases, while those of oxygen and the metalloids (" non-metals ") were termed acids. He held oxygen to be an essential constituent of all acids, and gave it its name (acid producer) accordingly. Berzelius modified these views by as- suming that oxygen was the most electro-negative element, all others being electro-positive with respect to it. The acidic or basic properties of the oxides, therefore, depended upon the excess of negative electricity possessed by the oxygen or of positive electricity possessed by the combining element; this view again required the presence of oxygen in all acids. The halogen acids, such as hydrochloric (muriatic) were sup- posed to be compounds of hydrogen and a halogen ; the latter substances were assumed to be oxides of hypothetical elements. However, since the halogens had never been split up into simpler substances, they were, according to Lavoisier's definition of an element, elements, and efforts were soon made in the case of chlorine to decide whether it was really a com- pound. About 1810 Gay-Lussac and Thenard, in France, and Davy in England, made attempts to decompose that gas in various ways, but without any success, and Davy decided that it was an element, and gave it its present name in distinction to Berthollet's misleading title of " oxymuriatic acid ". He pointed out that in the following three reactions it behaved exactly like an elementary substance : — i vol. Hydrogen + i vol. Chlorine —> 2 vols. Hydrochloric Acid, i vol. Hydrochloric Acid + Sodium -> Common Salt + £ vol. Hydrogen. Sodium + Chlorine — $> Common Salt. Gay-Lussac and Thenard also adopted this opinion, but Berzelius held out against ' it for a long while. It naturally NOTES ON THE HISTORY OF ELEMENTS 61 spoiled the oxygen-acid theory; it helped to overthrow the dualistic hypothesis. Davy himself, as a matter of fact, stated that hydrogen and not oxygen was the essential constituent of acids, since anhydrides (e.g. iodic anhydride) were not acid except in presence of water. The next notable point in the history of acids came several decades later, and consisted of Graham and Liebig's work (already referred to, p. 52). Graham showed that phosphoric and arsenic acids each exist in three forms, according to whether one, two, or three molecules of water were combined with one molecule of the acid anhydride. Liebig proved a similar fact a little later, when he showed that many organic acids (citric, cyan uric etc.), were poly basic. In this case the dualistic explanation, based on the addition of fresh molecules of water, was cumbrous, and Liebig soon saw that a clearer view was obtained by the hydrogen-acid theory, the polybasi- city being explained by the presence of more than one re- placeable hydrogen atom. This was really the first contribution to the modern theory of valency. After the general adoption of the hydrogen-acid theory (about 1855) there is little to be recorded in the development of views in this direction, except that Arrhenius' ionic theory extends the conception still further by suggesting that the 'characteristic properties of acids are due, not to elementary but to ionic hydrogen, H+. At the present day. the most general definition of an acid is a substance containing hydrogen re- placeable by metals, an expression which includes many organic __ CO\ bodies (e.g. phthalimide | . 1 _ NH, malonic ester ~~ CH2(COOC2H5)2, etc.), and also such metallic hydroxides as A1(OH)3, Zn(OH)2, etc., which form sodium salts in presence of alkali. The following acids deserve special attention : — • 62 A SHORT HISTORY OF CHEMISTRY Sulphurous. — Properties of burning sulphur known to Homer and Pliny ; SO2 isolated by Priestley. Sulphuric. — Known to Geber ; preparation from iron vitriol described by Basil Valentine. Nitric. — Known to Geber ; method of preparation by Basil Valentine ; constitution due to Cavendish. Carbonic. — Known as a distinct gas to Paracelsus and v. Helmont ; con- stitution due to Black and Priestley. Muriatic. — Known to Basil Valentine (spiritus salts) ; preparation from salt and vitriol by Glauber. Aqua regia. — Known as a mixture of aqua fords and spiritus salis to Basil Valentine. Phosphoric. — Discovered by Boyle (1693) ; investigated by Marggraf, Scheele, Gahn. Boric. — First prepared and its salts characterised by Homberg (1702). Hydrofluoric. — Used for etching glass by Schunhardt (seventeenth cen- tury), but without knowing its constitution ; worked out by Gay- Lussac and Thenard, Berzelius, Ampere; first prepared pure in 1869 by Fremy. The acids and anhydrides of chlorine (HC1O, HC1O3, HC1O4) were investigated by Davy, Balard, Roscoe and others during the first half of last century, but it is comparatively recently that their constitution and that of other halogen oxy- acids has been systematically explained by the progressive increase in valency (from one to seven) of the halogen. The majority of the more complicated inorganic acids (ferrocyanic, sulphocyanic, polythionic, etc.) have only been studied within the past century. Gay-Lussac and Davy were among the first workers in this field ; Balard, Liebig, Wohler, and Roscoe are other prominent names which must be mentioned. Attention should be paid to the numerous researches on " per " acids (cf. p. 72) carried out during the last few decades. § 2. Basic Oxides and Metallic Salts — The knowledge of metallic oxides has for the most part grown parallel with that of the acids ; the characteristic properties of alkalies (the stronger bases) were known to the 'earliest alchemists, while Lavoisier defined bases as the oxides of the metals, and Berzelius assumed them to be substances in which the electro-positive strength of the metal overcame the electro-negative force exerted by the oxygen. The possibility of polyacid bases fol- lowed as soon as the doctrine of polybasic acids was established NOTES ON THE HISTORY OF ELEMENTS 63 by Graham and Liebig, while finally, with the advent of the ionic theory, the characteristic reactions of bases were seen to depend on the presence in solutions thereof of the hydroxyl ion OH~. The term " base " extends of course to-day to all substances capable of possessing such an ionizable hydroxyl group, for instance, ammonium hydroxide NH4OH, pyridinium /°\ HC | CH C5H5NH.OH, sulphonium hydroxides R3S(OH), II — O- I HC CH \c^ phosphines R3P, py rones and so on. Curiously enough, the modem view of a salt was practically arrived at during the phlogistic period through the work of Rouelle and Richter. Rouelle (1744) defined salts (neutral, acidic, and basic) as the substances formed by the union of an acid and an alkali, and Richter (1791) discovered the laws governing the neutralization of acids and bases (cf. p. 32). It was therefore simply necessary for Lavoisier to adjust the terms to his new oxygen theory, and to point out that in his system salts were ternary and not binary compounds like the acidic and basic oxides. Berzelius also explained salt-formation as the result of the union of electro-positive and -negative oxides, pointing out the apparent confirmation of his theory in the electrolytic resolution of salts (such as sodium sulphate) into acid and alkali. He tried to account for double salt formation and the existence of water of crystallization by the assumption that even in salts there remained a slight excess of one or other kind of electric polarity. The final modern view of salt for- mation may be illustrated by the typical ionic equation : — R++ OH - + H+ + X~ =-R+ + X" + H2O. base acid salt Before glancing at a few bases and salts of historic interest, we may discuss the relations of the alkaline carbonates to the 64 A SHORT HISTORY OF CHEMISTRY alkalies. This was a source of great misunderstanding to the alchemists and phlogistonists, many of whom seemed to look upon the alkaline carbonates as elementary bodies which passed into the alkalies (alkaline calces), e.g. : — Chalk + phlogiston — > lime. Lime (i.e. chalk + phlogiston) + potassium carbonate — $> caustic potash + chalk. The researches of Joseph Black (1755) cleared up the whole matter, for he showed that : — (a) Limestone or chalk lost weight by calcination and yielded a gas ("fixed air") identical with van Helmont's " gas sylvestre". (b) The " mild alkalies " (alkaline carbonates) could also be made to yield this gas by the application of acids. (c) The "mild alkalies" on treatment with lime became "caustic," and at the same time chalk was formed in the proportion of chalk : lime, as had been found in the reverse direction in experi- ment (a). These results led him to the modern interpretation of the relations subsisting between lime and chalk, magnesia, and magnesium carbonate, and the "caustic" and "mild" alkalies. The following description of the discovery of the more no- table metallic oxides and salts may, although not exhaustive, be of interest : — The Ancients were acquainted with soda and potash, lime and magnesia, and the corresponding carbonates ; iwith rock salt, saltpetre, copper, vitriol, alum, cassiterite (SnO2) and others of the more plentifully occurring minerals. Naturally, however, there was little or no distinction drawn between closely allied bodies such as soda and potash or limestone and magnesite ; magnesia, alum, and lime were not definitely distinguished by the alchemists or iatro-chemists, and it was not until Scheele's time that baryta ceased to be regarded as a casual variety of lime. As might be expected from the development of experimental research during the alchemical era, a great many artificial preparations, as well as numerous naturally occurring compounds, were discovered by the metal- transmuters and their successors, the iatro-chemists. To the first alchemical period belong the discoveries of ammonium chloride (salmiac, Geber), carbonates (from urine ; and, by Basil Valentine, from salmiac and potashes), NOTES ON THE HISTORY OF ELEMENTS 65 copper oxides, acetate (verdigris), and sulphate (preparations by van Helmont and Glauber), silver nitrate (lunar caustic), gold chloride (from aqua regia and gold) ; of calcium sulphate (gypsum, etc.), mercuric oxide (Geber), mercurous chloride (calomel, Geber, improved later by Croll), cor- rosive sublimate (Geber) ; of the various alums (Basil Valentine ; all these were much confused with each other and with iron vitriol, FeSO4), lead oxides (litharge and minium), sulphide, and carbonate (white lead, with which various salts of zinc were confounded). The oxides and acids of arsenic were known to Geber and Albertus Magnus, and Basil Valentine investigated numerous compounds of antimony and of iron. The iatro-chemists were responsible for the investigation of sodium sulphate (sal mirabilis, Glauber, 1658) ; zinc oxide (Libavius), chloride (as an oil, Glauber), sulphide (Agricola) and sulphate (vitriol), distinguish- ing these from the similar lead compounds ; mercuric sulphate (turpeth, Paracelsus) ; stannic chloride (spiritus fumans Libavii, Libavius), lead and ferric chlorides (Glauber), and the lead acetates (Libavius). During the phlogistic period a considerable amount of the confusion between similar compounds such as potassium and sodium sulphates or lime, magnesia, baryta and alum was removed, and a clearer knowledge of the following amongst many other substances resulted ; the sulphates of potassium, magnesium (Crew, 1695), aluminium and iron ; calcium chloride and nitrate ; strontium carbonate (strontianite, Crawford, 1790) ; the various oxides of manganese (Scheele, and much later, in the nineteenth century, Liebig and Wohler, Mitscherlich and Franke) and of iron (Proust, and comparatively recently, Fremy on ferrates). We thus arrive at the modern epoch of inorganic chemistry, in which a most prominent part was played by Berzelius and his students. These very thoroughly investigated, from about 1820 onwards, the compounds of titanium, zirconium, thorium, chromium, molybdenum, tungsten, uranium, and other then recently discovered metals ; Roscoe also added to the knowledge of the halides of tungsten, while its complex oxy-acids received attention from Margueritte, Marignac and 6thers. We may also mention, amongst a mass of other work, the researches on copper sub-oxides (Rose and The"nard), on silver sub- and per-oxides (Wtfhler), and on the complex ammonia-metallic salts of cobalt (Rose, Fremy, Jb'rgensen, and latterly Werner), chromium (Christensen, Pfeiffer), rhodium (Jorgensen), iridium (Leidie) and platinum (Magnus, Jorgensen). § 3. Mineralogy — Our historical survey of inorganic com- pounds would be incomplete without reference to the study of naturally occurring bodies as distinct from those manufactured in the laboratory. Of course in olden times the overwhelming 5 66 A SHORT HISTORY OF CHEMISTRY bulk of substances known were minerals (limestone, marble, rock salt, etc.), since experiment played such a minor part in the chemistry of the ancients. Various ores and precious stones became known as time went on, and when, at the close of the phlogiston era, the importance of gravimetric analysis was realized, several chemists of note found scope for their energies in laborious but necessary analyses of the minerals then known. Bergman, Scheele, Klaproth, Fourcroy, and Vauquelin gave especial assistance in this field, their researches showing that minerals obeyed the same laws of constant and multiple propor- tions as synthetic compounds. At this time, too, efforts were made to classify minerals, but chiefly according to their physical properties, their chemical relations being almost neglected. The most noteworthy of these earlier mineral systems were those due to Werner and to Ha'uy of Paris, towards the end of the eigh- teenth century. The latter based his classification chiefly on similarity in crystal form (cf. " Crystallography," chap. x.). Bergman, on the other hand, emphasized the importance of the chemical composition of minerals, although in his day so little was known of this side of the question. The most thorough classification of minerals, however, was due to Berzelius, who in 1812 showed that their composition was in entire agreement with Dalton's atomic theory, and that they were inorganic compounds of exactly the same order as any prepared in the laboratory. In 1824 he produced a mineral system, based on the dualistic hypothesis, dividing minerals into non-oxidized and oxidized compounds. Although various modi- fied classifications have since appeared from time to time, these present no fundamental difference from that of Berzelius. The nomenclature of minerals has never been properly sys- tematized, for they are still named according to individual peculiarity, or to the locality where first found, or in order to perpetuate the names of their discoverer or his friends, but rarely so as to show somewhat of their chemical composition. During the past 100 years mineralogy has been characterized NOTES ON THE HISTORY OF ELEMENTS 67 by attempts to synthesize minerals (a kind of chemical geology) and by the systematic investigation of newly discovered ones. Amongst the synthetic efforts must be mentioned the con- version of chalk to marble (Hall, 1 80 1), the artificial preparation of arragonite (G. Rose), Bunsen's researches on the geysers of Iceland, Van't Hoff's studies with reference to ocean deposits, and, finally, the comprehensive work of a school of French chemists, represented by Senarmont, Levy, Friedel, Berthelot, and Moissan. These have reproduced in the laboratory the formation of quartz, etc., by slow double decomposition in solution ; the slow crystallization of dilute solutions (gypsum, etc.) ; the action of water under high pressure at varying tem- peratures ; and the formation of minerals in the interior of the earth or in prehistoric times by the action of intense heat, with or without an accompanying enormous pressure (Berthelot, Moissan) ; the preparation of carbides, nitrides, etc., in the electric furnace, the interchange of allotropic forms of the elements (e.g. production of small diamonds, etc. etc.). New minerals have been found both as the result of geo- graphical exploration and of more thorough examination of previously known deposits. ' Examples in the first category may be taken from the discovery of platinum and allied ores in South America, of new ores (along with tin and other known metals) in Borneo, of gold in various continents (Africa, Aus- tralasia, North America), and (recently) of numerous rich de- posits of silver, cobalt, and many other metals in Northern Canada. Berzelius and his co-workers discovered many ores containing chromium, molybdenum, vanadium, and allied metals; Mosander in 1841, and many workers since, have investigated the ores of yttria, gadolinite, etc., occurring chiefly in Scandinavia . and Greenland. About fifty years ago the deposits of soluble salts at Stassfurt (near Magdeburg) were discovered, and have been extensively utilized in many ways (manures, preparation of magnesium, potassium, etc.) ; they consist mainly of chlorides 6S A SHORT HISTORY OF CHEMISTRY and sulphates of potassium, magnesium, sodium, and calcium. Of late years a notable class of minerals has been studied, viz. those containing occluded gases, usually hydrogen, nitrogen, carbon dioxide, helium, and sometimes argon and neon-(cleveite, malacone, gadolinite, etc.). The chemical examination of meteorites must not be forgotten, since this has confirmed the spectroscopic evidence that extra-terrestrial bodies are for the most part made up of the same elements as our own planet (Wohler, Wolcott Gibbs). § 4. The Chemical ^Elements — The preceding paragraphs will have shown clearly that in the majority of cases the dis- covery of an element was long preceded by a knowledge of its compounds, and that, further, the presence of a previously overlooked element has often been realized a considerable time before chemical methods were sufficiently advanced for its isolation (e.g. sodium, calcium, lithium, vanadium, fluorine, etc.). On pp. 69, 70, we give a table of the elements (grouped according to the periodic system) showing the circumstances of their discovery, and, when not isolated by their discoverer, of their isolation. A few isolated points in the history of inorganic compounds remain to be dealt with. The existence of different forms of the same substance (e.g. charcoal, graphite, diamond) has been investigated by imany workers since Berzelius characterized such phenomena as a particular form of isomerism. The term "allotropy" was introduced about 1841. It has latterly been realized that such inorganic isomers are probably caused by polymerism (difference in molecular weight) or polymorphism (difference in crystalline form, probably due to difference in molecular structure). Besides oxygen and ozone (Schonbein, 1840), the following cases of elementary allotropy have been studied : sulphur (Mitscherlich, 1852), selenium (Berzelius, 1817; Hittorff, 1851), boron and silicon (Wohler), tin (Rammelsberg, 1880). There are probably more cases of allotropy in the realm of compounds than of elements, but comparatively few of NOTES ON THE HISTORY OF ELEMENTS 69 Isolated. 5 Bunsen (by electrolysis). 7 Davy (electrolysis of moist hydroxide). 7 Davy (electrolysis of moist hydroxide). i.S § ^ §1 K « •3-8 » *" •S S . c « „• 'rt^.2 U C l-ili^l ti^llf l^l -I! oo oo op 8 Davy and Gay-Lussac (independently). 7 Wohler (K on the chloride). 5 Berzelius (K on fluoride). 4 Berzelius „ 8 Berzelius. o Berzelius in o o o CM o Q M MM N M «cg H w oo 00 M oo oo H M 00 H » H oo oo oo MM H 00 H "— -r-— ^ , , £ Pf rt rt rQ -^ rt -=>*-5 g £ e& S x-S S otice of Cc y times inction fro irchhoff(fi means of 1 R 1 -o g *u Hi >.% t> 1 —v'rt ^I'S £ $£* Is" i& H rsT 'o rt 0 O^, 4> ||| Ill . jj r ^ rt to »£ *5 $*'§ c S J3 to gO 1 "to -2 G ,.y t> ffi 2 3 ° -^ v *O •T3 _ rt ^ C to •« Q 1) f* *X3 ,£^ »r5 rS ^ C^H 9^ C ry^ O ^ IO §^ , «- J3 Sr- ^^ CC T3 w o — ^8 ^O ^ II uhamel ll 2 «U 8S.1 .SjS^ *q3 r^l o ^* 1 gll rt SJ w i3 s|J 1 If || 1 1 5 3 K «-s P -a iifii - <£ Q 51^ J^jy: u£ ffi SnJ pg<5 O Ui ^ CQ ^ 1^ o H O O ^ r^ in t^ ^ c> N . in Ol M t>. vo 00 O 00 o in t^ 00 00 r^ f^oo oo & M >• % H M H W 2-5*88 o m H Tj-OO t^cc inoo n O^ N r>, O O rn N t^ O • O H o H' 01 00 O M0 £3-0 ro a""" * CO 00 fOO O Oi TJ-OO co of O1 M §* H ^^ af cb b b CN N •* o> ^ cr> w cJo 0 ^ 111 Sill JOG Potassium IE. ^•2 g.*- Is III Calcium Strontium Barium ill s 111 1 g ^Jg-i Mercury Scandium § i Aluminium Gallium Indium Thallium iifjl HNUHO Silicon O A SHORT HISTORY OF CHEMISTRY c2 's^-S II r* Hri re-t ^ 55 > 1) <; Q ^ NOTES ON THE HISTORY OF ELEMENTS 71 these (e.g. the iodides and sulphides of mercury) have been minutely studied. The hydrides of the elements form an interesting series ; those of the alkaline and alkaline earth metals are of compara- tively recent discovery, the rest are mainly non- metallic. The most noteworthy are those of boron (B3H3, Ramsay and Hat- field), silicon (SiH4, Wohler, 1857 ; Si2H6, Moissan and Smiles, 1902), sulphur (H2S, Rouelle ; H2S2, Scheele), and the nitrogen group, which merit special attention : — SfH3 NH(OH)2 N2H4 N3H AsH3 SbH, Ammonia Compounds known to the ancients ; gas discovered by Priestley, 1774. Discovered by Lessen, 1865 ; obtained pure by Lobry de Bruyn and by Crismer, 1891; sulphonic acids studied by Lossen, Divers, etc. In solution only ; Angeli, 1907. Discovered by Curtius,i887 ; obtained pure by Lobry de Bruyn, 1896. Discovered by Curtius, 1890; also obtained by W. Wislicenus, 1892. Gaseous phosphoretted hydrogen Discovered by Gengembre, 1783. Liquid phosphoretted hydrogen „ The"nard, 1845. Arsine ,, Scheele. Stibine „ Soubeiran, 1830. Hydroxylamine Dioxyammonia Hydrazine Hydrazoic acid, azo-imide The oxides and oxy-acids of nitrogen, phosphorus and sulphur are worthy of note : — N20 Nitrous oxide N20.jH.2 Hyponitrous acid NO Nitric oxide N2O:; Nitrogen trioxide N0.2 ,, peroxide N^O-, ,, pentoxide H3P(X Phosphorous acid H4P2Or, Hypophosphorous acid SO3 Sulphur trioxide SaO, Sulphur sesquioxide Davy, 1806 (" laughing gas "). Divers, 1871 ; ThieleandLachmann, 1895 ; Hantzsch, 1896. Priestley, Dulong, Pe*ligot. Dulong, 1816; Peligot, 1841. Dulong, Gay-Lussac. St. Clare Deville, 1849. Lavoisier ; Wurtz, 1849. Salts by Dulong, 1816. Isolated by Dobereiner. „ Weber, 1864. A SHORT HISTORY OF CHEMISTRY H2SaO3 Thiosulphuric acid H2S(n)O6 Polythionic acids (n = 2 to 5) Hyposulphurous acid Salts by Gay-Lussac, 1819 ("hypo- sulphurous acid "). Investigated since 1840 by Wacken- roder, Spring, etc. H2SO2, Schutzenberger, 1869 ; H2S2O4, Bernthsen, 1900 H4S2O5, Bucherer, 1904. There are also several substances of interest related to hydro- gen peroxide : — O3 Ozone Discovered by Schonbein (1840) ; con- stitution by Marignac, Andrews and Soret ; much used of late in organic chemistry as oxidizing agent. Discovered by ThSnard (1818) ; an- hydrous, Wolffenstein (1894). Isolated by Berthelot, 1878 (SO2 + O2 under silent discharge). Only known in dilute solution ; K2S2O8, electrolysis of KHSO4 (Marshall, 1891). Isolated by H. Caro (1898) ; used by Baeyer as organic oxidant ; H4S2O9, Armstrong and Lowry, 1902. Obtained by electrolysis of MHCO3 (Constan and Hansen, 1897). H2O2 on chromic acid solution (Barreswil, 1847; Moissan, Ber- thelot) ; boric, molybdic, tungstic and uranic acid salts all yield peracids with H2O2. Finally, there are a number of halides of the elements whose discovery presents points of interest : — H2O2 Hydrogen peroxide S2O7 Persulphuric anhydride H2SaOg Di-persulphuric acid H2S05 Mono-persulphuric acid M^CaOg Percarbonates KCrO5,H2O2 Potassium perchromate BX3 SiX4 Boron halides \ Silicon halides } Nitrogen chlorides Nitrogen iodides Investigated mainly by Berzelius, Wohler and Deville. First studied by Dulong (1812) and then Gattermann. ,, Gay-Lussac. NOTES ON THE HISTORY OF ELEMENTS 73 Phosphorus trichloride First studied by Gay-Lussac (1800). ^Clg „ pentachloride „ Davy (1800). 'OClg ,, oxychloride ,, Wurtz (1847). JF5 ,, pentafluoride „ Thorpe (1876). \.sCls Arsenic trichloride „ Glauber. § 5. The Metals of the Rare Earths — There are a number of rare metals, for the most part occurring together in a few rare minerals of not very wide distribution (chiefly in Scandinavia and Canada), and these are characterized by great similarity in chemical, and in many physical, properties. In some cases chemical reactions do not suffice to effect their separation, which can only be accomplished by fractional crystallization of their salts, the process being controlled by spectroscopic examination. The following is a list of these elements, taken from the International Atomic Weight table for 1909 : — Element. At. Wt. Discovery. Scandium 44-1 1879 Nilson. Yttrium 89-0 1794 Gadolin. Lanthanum 139-0 1839 Mosander. Cerium 140-25 1803 Klaproth. Praseodymium 140-6 ) f 1841 Mosander (Didymium). Neodymium I44'3-' 1 1885 Resolved by Welsbach. Samarium *5°'4 l849 Lecoq de Boisbaudran. Europium 152-0 1896 Demarcay. Gadolinium 157-3 l889 Lecoq de Boisbaudran. Terbium 159-2 1843 Mosander. Dysprosium 162-5 l886 Lecoq de Boisbaudran. Erbium 167*4 J843 Mosander. Thulium 168-5 l877 Cleve ; 1906 Urbain. Ytterbium 172-0 1878 Marignac. Lutecium I74*° I9°7 Urbain. As previously remarked, this series is of great theoretical interest, since, as Crookes has shown (1885-9, etc.), it appears to comprise a number of elements which are far more intimately related to each other (" meta-elements," 1889) than is commonly the case, and may therefore throw some more light on the 74 A SHORT HISTORY OF CHEMISTRY problem of the genesis of the elements. In the meantime it must be pointed out that scandium, yttrium, lanthanum and perhaps cerium are the only members of the group which readily fall into line with the periodic system ; in connexion with this Benedicks (1904) has suggested that the metals with atomic weights intermediate between those of barium and tan- talum be interposed as a kind of transitional series between these two. It is noteworthy that this scheme tends to consoli- date the periodic table, leaving only eight vacant spaces. § 6. Radio-active Elements — Since the science of radio- activity came into being search has naturally been made for the elements which give rise most markedly to the phenomenon, and at the present time five such elements, all of them of very high atomic weight, are certainly known, viz. uranium, thorium, radium, polonium and actinium. In 1896 Becquerel noticed the radio-activity of uranium, and six or seven years later Madame Curie observed that of thorium, and also stated that it was only the product from natural sources (pitch-blende) which showed very marked activity, the effect being much stronger than any observed with pure laboratory uranium or thorium compounds. On the other hand, the latter showed about one hundred times as much radio-activity as any com- pound of other elements, and it was held to be doubtful whether any other element was at all radio-active. Mme. Curie, therefore, fractionally analyzed pitch-blende in an attempt to isolate the more radio-active constituents, and found that the radio-activity became concentrated in the barium and bismuth groups. She fractionated the chlorides from the barium precipitates, and finally obtained OT gm. pure radium chloride from a ton of pitch-blende. Giesel improved the method of fractionation by using the bromides instead of the chlorides, and so obtained 0-25 gm. pure salt from a ton of mineral. Mme. Curie determined the atomic weight of radium by precipitating the chloride with silver nitrate, and obtained the value 225, agreeing with the place assigned to radium in the NOTES ON THE HISTORY OF ELEMENTS 75 periodic system. Runge and Precht estimated the atomic weight later as 257*8, from spectroscopic calculations, but Mme. Curie's value has been confirmed (1908) by Haitinger and Ulrich, working with larger quantities of radium bromide. Mme. Curie and Debierne have very recently isolated radium as a white, easily oxidized metal by electrolysis of the fused salts, using a mercury cathode. Mme. Curie next worked up the precipitates of the bismuth group, and discovered a new element, polonium^ but did not succeed in isolating a pure salt. Marckwald (1903), however, prepared the element in a state of purity, but only obtained 4 milligrams from two tons of pitch-blende. Polonium was found to resemble tellurium. Finally, Giesel (1902) and Debierne (1903) discovered an element, similar to thorium or titanium, but more radio-active, which has been named actinium. CHAPTER VI THE HISTORY OF ORGANIC CHEMISTRY § i. Organic Chemistry: the Chemistry of Animate Nature — The knowledge of the laws governing the combina- tion of the chemical elements and the views held at the present day with respect to the final constitution of matter have been mainly derived from inorganic or mineral substances, while the theories of how the atoms are linked together in a compound are based upon what has been discovered during the past cen- tury with reference to organic substances, or, in the nomencla- ture of Lavoisier's time, bodies of animal or vegetable origin. Many simple organic compounds had of course been met with very early in chemical history ; marsh gas was known to van Helmont, alcohol (or, aqua vitae, as the alchemists thought best to call it), ether and several of the simpler ethyl esters (e.g. " sweet spirits of nitre ") were prepared and used medicinally and otherwise much before his time, while quite a number of organic acids (such as acetic, oxalic, benzoic) were known to the alchemists or phlogistonists, and to these Scheele added several more, discovered by him in various plant or animal juices (malic, citric, oxalic, prussic, tartaric, lactic, uric acids). All organic compounds known at the beginning of the nineteenth century were in fact directly obtained from animate nature, and of the more complicated substances a few sugars and plant bases were practically all that were known. Difficulty was found in accommodating the simple dualistic hypotheses of Lavoisier, Davy, etc., to the cases of such organic 76 THE HISTORY OF ORGANIC CHEMISTRY 77 compounds, and many thought that these were part of a distinct realm of chemical nature, subject to different laws. This and the source of all the organic substances then known together led to the idea that such bodies were only formed by the intervention of a special " vital force ". This view, which was also suggested by various workers, notably Bergman, in the previous (phlogistic) period, was rendered untenable when it was shown that in several instances pairs of substances of the same empirical composition — one recognized as " inorganic " and the other as " organic " (the terms bearing at that time their literal meaning) — were so closely related that one member could frequently be changed into the other. The discovery of isomerism, indeed, marks the commence- ment of our modern structural chemistry, and at this point the detailed description of its history must begin. In 1825 Faraday discovered a hydrocarbon, butylene, of the same percentage composition as Dalton's defiant gas, and shrewdly predicted that more instances of the kind would fol- low in connexion with carbon compounds. Somewhat earlier (1823) Liebig and Wohler proved the existence of two isomeric acids, cyanic and fulminic acids, and in 1828 the latter dis- covered the famous conversion of ammonium cyanate to urea. Again, in 1832, Liebig and Mitscherlich showed that Berzelius' sarcolactic acid from flesh (1807), and Scheele's lactic acid from sour milk (1780) possessed the same composition, and at about the same time Berzelius isolated racemic acid, of the same composition as Scheele's tartaric acid from argol. In 1831 Berzelius proposed the term "isomerism" and a year later subdivided it into two new ones, " polymerism " and " metamerism," which in the course of time became changed to "polymerism" (substances of the same empirical but dif- ferent molecular composition), and "isomerism" (different substances of the same molecular composition). § 2. The Earlier Theories of Structure of Organic Compounds — To understand the transition from this early 78 A SHORT HISTORY OF CHEMISTRY and somewhat chaotic state of affairs to the present tolerably well-ordered system of organic theory, we have to glance at a complicated series of hypotheses designed in succession to explain organic reactions. These may be roughly grouped as follows : — (1) " Radicle " theories. (2) " Type " theories. (3) The modern structural theory, which in some measure combines both the preceding. Since these temporary hypotheses were devised contem- poraneously with the various systems of atomic weights des- cribed in Chapter iii. the formulae used by their authors are very confusing, and so as far as possible the corresponding modern formulas are added in brackets in the resume of their work which follows : — (i) "RADICLE" THEORIES. Lavoisier's extension of his oxygen theory to include organic acids has already been mentioned ; he seems to regard these as oxides of " radicles " containing more than one element, and including in any case carbon and hydrogen. A more precise view of .a " compound radicle " was arrived at by Gay- Lussac (1815-22) as the result of his work on the cyanogen compounds, from which it was clear that the cyanogen group functioned as a " compound element " by forming a whole series of compounds, such as cyanogen hydride (HCN), chlo- ride, bromide, iodide, etc. Further support was given to the view that organic chemistry is the " chemistry of compound ra- dicles " by Liebig and Wohler's investigation of the " radicle of benzoic acid" in 1832. They prepared benzoyl hydride (benz- aldehyde), hydrate (the acid), halides, sulphide, ether and other compounds, thus showing that "benzoyl" CHH10O2(C7H5O) behaved in analogous fashion to a simple element. Berzelius strongly supported this first radicle theory^ since it con- THE HISTORY OF ORGANIC CHEMISTRY 79 firmed his own dualistic electrical hypothesis by extending it to organic substances. Several other radicles were inves- tigated in succeeding years, notably cinnamyl (1834, Dumas and Peligot), salicyl (1838, Piria), and cacodyl (1837-43, Bunsen), and the simple theory of organic radicles was generally accepted between the years 1837-40. Other observations of Gay-Lussac (upon the relations be- tween ethylene, alcohol and ether) led to Dumas and Boullay's etfierin theory. These authors tried to show in 1828 that ethylene (etherin) performed similar functions to ammonia as a compound radicle, in order to explain (on a " radicle " basis) the connexion between alcohol, ether, and allied compounds ; they pushed the analogy too far, however, by suggesting that ethylene was essentially a base like ammonia, and this brought more discredit than was perhaps fair to the original hypothesis, which looked upon alcohol, ether, and ethyl chloride, for instance, as the respective hydrate, oxide, and hydro-chloride of etherin. In 1834 Liebig and Berzelius parted company to a certain extent with respect to their views on organic structure. Berzelius was always tied down by his dualistic theory, which he seems to have placed before all other considerations. He insisted on regarding all oxygenated compounds as oxides, and so assumed that ether and alcohol were oxides of two different radicles (C2H5)2 and C2HG. Liebig on the contrary held that these were derivatives of the same radicle " ethyl," but ascribed to " ethyl " double its real molecular weight, whereas Berzelius was correct in this point, as will be seen from the following table : — Modern. Liebig, 1834. Berzelius, 1833. Alcohol C2H6O Ethyl oxide hydrate C4H10O . H2O (C2H6)O Ether C4H10O Ethyl oxide C4H10O Ethyl sub-oxide (C3H-)2O Finally, in 1838, Liebig tried to modify still further the con- ception of the structure of alcohol by taking what he called the " acetyl " radicle C4H6(CH3C — ) as his basis. A little con- sideration will show how this dehydrogenation of the ethyl 8o A SHORT HISTORY OF CHEMISTRY group permitted of the oxidation products of alcohol, aldehyde, and acetic acid, being classed as derivatives of the same group as that present in alcohol and ether. We may therefore sum up the period of " radicle theories " as : (a) a general adherence to the view that organic bodies are composed of radicles (groups of atoms) which function as elements and which are in general preserved intact through a whole series of reactions ; (b) a series of efforts to bring the simple compounds such as alcohol, ether, acetic acid and the like into line with the more distinctive and well-defined radicles such as benzoyl, cacodyl and cyanogen. (2) " TYPE " THEORIES. The fact which above all others tended to throw doubt upon the radicle theories was the substitution of hydrogen by chlor- ine in organic compounds. This phenomenon, which was impossible according to the upholders of the dualistic view, was observed by Gay-Lussac, Liebig and Wohler, Faraday, and Dumas in the respective cases of hydrocyanic acid, benzaldehyde, ethylene and alcohol (to chloral), and in 1834 the last-named worker summed up the facts in his Laws of Substitution (or metalepsy, to use his own term). In 1837 Laurent made an attempt, to some extent temporarily successful, to reconcile the radicle theories with the new substitution laws by suggesting that the radicles could be altered to a certain degree by sub- stitution, but that there always remained a nucleus (of carbon and hydrogen) which was unalterable. This satisfied neither Berzelius nor Dumas, although it prob- ably approaches the modern structure theory more nearly than the views adopted by either. A few years later, in 1840, Dumas published a new theory which supplanted the dualistic by a unitary view, each compound being regarded as a complete whole in itself, its components being related in analogous fashion to the worlds of a planetary system. At the same time THE HISTORY OF ORGANIC CHEMISTRY 81 he attempted to classify compounds from their reactions ac- cording to definite " mechanical types" (a method also suggested by Regnault), and further asserted that substances closely re- lated in properties belonged to the same " chemical type" gene- ral structural similarity without necessarily similar properties being the criterion of inclusion in a given " mechanical type ". An illustration will make this clearer : — 4 Chloracetic acid^C^A jChemical type. Thus there was no definite view held with regard to organic constitution in the beginning of the forties, and as this was also the period (cf. chap. iii. p. 37) when no fixed rule had been adopted by which to determine the true relation between atomic weight and equivalent, there was considerable confusion in almost every department of chemical theory. The criticisms of two French chemists, Laurent and Gerhardt, upon this point almost remind one of the scathing words of Kunkel and Boyle with reference to the charlatan alchemists. Laurent in 1843 precisely defined the terms atom, mole- cule, and equivalent, by means of a more rigid application of Avogadro's rule than had hitherto been made. Gerhardt and Laurent together made it their work to develop the unitary view of organic structure, as opposed to the dualism of Berzelius and many of the German chemists. A preliminary to this advance was Gerhardt 's " Theory of Residues" propounded in 1839. Any organic reaction which can be represented as a binary one, e.g. — C2H3OC1 + NH3=C2H3ONH2+ HC1, must, in order to satisfy the observed differences between ordinary inorganic double decomposition and the reactions of carbon compounds, be explained theoretically on a different basis (for the sake of clearness it may be pointed out that in our time the characteristics of most inorganic double transpositions 6 82 A SHORT HISTORY OF CHEMISTRY are considered to be due to the presence of the reacting sub- stances in the form of ions, the two classes of reactions being thus ionic and non-ionic). Gerhardt's explanation was that in such binary reactions the inorganic parts of the molecules inter- acted in the ordinary way and the residual (organic) parts then joined to form the new organic substance. A substance so formed was called a "copulated" compound — formed by the linking together of the two residues. Thus C]iH3OCl (Acetyl chloride) + NHS = HC1 + QH3O| (Acetamide). He next availed himself of the results furnished by Liebig and Graham respectively on polybasic organic and inorganic acids, and his efforts to explain these in a similar manner led, in 1 844, after Laurent's all-important threefold definition recalled above, to a much simplified scheme of atomic and molecular formulas, and especially to the first systematic classification of organic compounds, carried out jointly by these two workers. It is interesting to recall that Gerhardt defined organic chemistry as the " chemistry of the carbon compounds " rather than of " compound radicles," and that he pointed out the general recurrence of homologous series (already hinted at by Schiel (1842) for alcohols and Dumas for acids), and the existence of isologous series (the corresponding compounds of similar chemical nature in different homologous series, e.g. alcohol and phenol, propyl alcohol and the cresols) and of heterologous series (which are practically the same as Dumas' " mechanical types " (loc. cit.)). The next definite advance was the evolution of four general types by Gerhardt in 1853, based fundamentally upon Hi J Hi Hi hydrogen TT [-, hydrochloric acid p, [-, water TT [O, and HI H ammonia H >K. (A fifth type, methane ^ [C2(C = 6), was H' Hj afterwards added by Kekule.) THE HISTORY OF ORGANIC CHEMISTRY 83 The events of the intervening nine years between 1844 and 1853 contributed a great deal to this further systematization, and must be briefly summarized. In the first place, Kolbe and Frankland engaged upon a series of researches in order to modify the old Berzelian theory so as to make it accord with all the new facts then known. In 1845 Kolbe had prepared trichlormethyl sulphonic acid CC13 . SO3H, and the corresponding mono- and di-chloro^acids, so that a series of sulphonic acids entirely analogous to the fatty acids from acetic to trichloracetic was formed, and in 1849 Frankland prepared numerous organo-metallic derivatives (from the metals and alkyl iodides) which (by interaction with water) readily yielded substances believed at that time to be the " radicles " themselves ; at the same time these chemists jointly investigated the saponification of nitriles to fatty acids and the action of potassium on ethyl cyanide (yielding ethane, but the product was not recognized owing to some experimental error). Finally, in 1850 Kolbe electrolyzed the salts of the series of fatty acids and believed he had isolated the radicles of the acids (in reality, of course, the products were hydrocarbons formed by union of two radicles, e.g. COOK K ^v^fvyrv. rv. /• »v COOK -* K + 2C02 + C2H6'' They believed they had thus shown : — (a) the importance of the alkyl radicles in determining the character of a compound (e.g. CH3~, CH2C1-, CHC12-, CC13-). (^) the existence of the radicles themselves. (c) the fatty acids to be " copulated compounds " l of oxalic 1 Kolbe and Frankland used " copulated compound " in the sense given to the term by Berzelius, which differed from that in which it was used by Gerhardt, for Berzelius apparently simply meant that in a "copulated compound" a neutral group was joined to an electro-positive or negative group. 84 A SHORT HISTORY OF CHEMISTRY H20 acid and the alkyl radicles (since (CN), -- >(COOH)2, and R . CN— ->R . COOH). Much later, in 1857, Kolbe suggested that carbonic acid served as the fundamental type of organic acid, showed how aldehyde, alcohol, and hydrocarbon types could be derived therefrom, and proved there was some truth in his view by predicting the existence and properties of formaldehyde and of secondary and tertiary alcohols, then unknown, but discovered soon after ; e.g. aHO.(CA).Oa HQ . (CA). 02 H.(CaOa),H HO.C2H3, O Carbonic Acid Formic Acid Formaldehyde Methylalcohol (HO . CO . OH) (H . CO . OH) (H . CO . H) (HO . CH,) On the other hand, much experimental work was accumulated during this decade which strengthened the " theory of types ". The outstanding features are : — 1849 Wurtz. Formation of amine bases from cyanic esters and ammonia. 1850 Hofmann. Formation of ammonium or aniline bases from alkyl iodides and ammonia or aniline. (Cf. 1845, The"nard's preparation of analogous phosphine bases.) 1850-52 Williamson. Preparation of ether from ethyl iodide and potas- sium ethylate. The last-mentioned was perhaps the most important of all, for it demonstrated that ether bore the same relation to alcohol as an alkaline oxide to its hydroxide (a connexion previously suggested by Laurent in 1846). Williamson was thereby enabled on a similar basis to explain the much-discussed mechanism of the preparation of ether from alcohol and sulphuric acid (previously ascribed by Mitscherlich, Berzelius, and others, in default of anything better, to " catalytic action "), and to suggest that alcohols, ethers, acids, and their THE HISTORY OF ORGANIC CHEMISTRY 85 derivatives all belonged to one and the same "water type" TT"| lO. The preparation of acid anhydrides from acid chlorides HJ and fatty acid sodium salts by Gerhardt, in 1852, came as an excellent confirmation of this theory. A little later (1854) Williamson and Kay gave a further example of the fruitfulness of this " type " hypothesis by syn- thesizing the first dibasic alcohol — glycol, from ethylene iodide — its existence having become probable, since they had recently prepared orthoformic ester, and Berthelot had just shown gly- cerol to be tri-basic, these being the first instances Q{ tri-basic alcohol derivatives known, thus leaving a gap which was filled by glycol. In the meantime it had become customary to refer the ammonium bases of Hofmann and Wurtz to the " ammonia type," and Williamson suggested that combinations of these, yielding " mixed types," occurred in the more complicated com- pounds. It will be noticed that the term " mixed type " is more or less synonymous with Gerhardt's view of a " copulated compound ". For example : — H Acetic Acid Ammonia, Amidoacetic Acid He also extended the idea to inorganic acids and bases, though not with such great success as on the organic side. Kekule's first paper in connexion with organic structure (in 1854) dealt with the extension of Gerhardt's simpler types to an extended series of mixed types. It will be seen that Gerhardt's generalization was a combina- tion of those parts of the older radicle and type theories which had survived the test of application to the numerous new facts discovered between 1830 and 1850, and, further, that the next development (the idea of atomicity or valency) was a very gentle transition from the four main types : — 86 A SHORT HISTORY OF CHEMISTRY Hl a; H. It will be useful to give a table of the different advances made in each of the two kinds of structure theories : — Radicle. Type. 1822 " Cyanogen " (Gay-Lussac). 1834 "Laws of Substitution" 1832 "Benzoyl" (Liebig and (Dumas). Wohler). 1837 Nucleus theory (Laurent). 1832 The older radicle theory 1840 Type theory (Dumas). (Liebig and Wohler, Ber- 1839 Theory of Residues (Ger- zelius). hardt). 1828 Etherin theory (Dumas). 1834-8 New radicle theory (ethyl andacetyl theories, Liebig). 1844 Gerhardt and Laurent's classification. 1848-50 Evolution of ammonia type through Wurtz's and Hofmann's work. 1850-2 Evolution of water type through Williamson's work. 1853 Ger hardt' s general type theory. 1854-7 Williamson's and Kekule's " mixed types ". § 3. Saturation Capacity and the Modern Structure Theory — Kekule saw that the use of " mixed types," such as |H N H CO\ implied the presence of polybasic radicles, and in 1857 was able to give definitions of mono- di- and tri- basic radicles according to the types in which they occurred. Several years earlier, however, Frankland reviewed the results of his work on organo-metallic compounds, and on comparing these with inorganic compounds of the same metals, it was seen that each metal possessed a " maximum saturation capacity," i.e. could combine with a certain definite maximum number of monobasic (or to use the clearer term, monatomic) groups, and no more. This observation led in one direction towards the periodic classification of the elements, and in another to the establishment of the valence theory. These views upon saturation-capacity, or atomicity or com- THE HISTORY OF ORGANIC CHEMISTRY 87 bining power were extended to the case of carbon indepen- dently, and almost simultaneously, by Couper and Kekule" in 1858. Couper showed that carbon possesses four combining units, and elaborated a system of graphic notation of the chief carbon compounds, which is practically that in use at the present day, except that he retained the atomic weight of 8 for oxygen, and, consequently, all his oxygen atoms are doubled. A couple of examples will show the similarity of his formulae to ours : — cr o o jc c o OH Ether j I 2 2 ' I ; tartaric acid j » /^ TT TT /"* *..••••*! (^t±3 w3u L, o OH 1 O OH C TT Kekule's memoir on the subject is on much the same lines, and, after establishing the quadrivalence of carbon, goes on to explain the nature of the more complicated organic compounds, showing how these may be built up of chains of carbon atoms with the other elements attached to the atomic combining units remaining free after two had been used up in the union with neighbouring carbon atoms, e.g. : — I I I I I I Thus, in about five years after Gerhardt had united all that was best in the radicle and type theories, his efforts had led to the further development which soon ended in the evolution of our present structural ideas. It has been said that Couper originated the modern structure formula in its present form ; Kekule devised a system of graphi- cally representing the atomicities of the elements by the size of the symbols, but, like Dalton's system of atom symbols half a 88 A SHORT HISTORY OF CHEMISTRY century before, it was found too cumbrous for daily use. Crum Brown introduced the method of representing the graphic formula of a compound, which is next illustrated, in 1865 :— © © © © II II ®-©~©—©-©-©—® i i il © © © © and, by leaving out the circles, Erlenmeyer and Frankland reduced the notation a year or two later to the form it now holds. § 4. Benzene and the Cyclic Compounds — The reader will have noticed that the compounds whose constitutions were gradually denned by the long succession of hypotheses cul- minating in the Frankland-Couper-Kekule valence theory were all of the simplest kind — methane, alcohol, citric acid, oxalic acid, and the like, or, in a word, the " simpler fatty compounds ". Groups like benzoyl and cinnamyl and the aniline residue were still written empirically, C7H5O, C9H7O, C6H5N, and so on, and no further insight was gained into their ultimate composi- tion. The benzoyl and cinnamyl radicles were among the first of this class to be discovered, and so, since these were obtained from various " essential oils," their designation (aromatic) be- came extended to the whole series of bodies chemically related to them. During the ten years 1858-68, also, much progress was made in extending the classification of fatty compounds and in dis- covering new compounds and preparative methods based on applications of the valence theory, while the study of the aromatic compounds was always hampered by the ignorance of their THE HISTORY OF ORGANIC CHEMISTRY 89 fundamental constitution. It was soon made clear that any theory which would explain the facts must account for the comparative richness in carbon of the aromatic series, for the circumstance that no known aromatic compound contained less than six carbon atoms, reduction of this number leading to loss of the characteristic properties displayed by the series, and for a general resemblance in chemical behaviour running through the whole series and distinguishing it from the fatty com- pounds. The credit of establishing such a theory belongs in this instance entirely to Kekule (the valence theory, it will be recalled, was divided between Couper and Kekule). In 1867 he stated that all the observed facts could be satisfactorily explained by as- suming as the characteristic structure of such compounds a nucleus of six carbon atoms united in a ring, each atom having its valencies so disposed as to admit of union with only one monovalent element or group. Benzene, the simplest member (discovered by Faraday in 1825), was therefore formulated as : — H— C(6) <2)C— H (5) (3) C— H — H— C The success of his theory may be best judged by its results : the state of affairs in 1867 has been so materially altered that at the present day more aromatic than fatty substances have probably been synthesized in the laboratory. The idea of a closed carbon chain was not only applied to the substances then called aromatic, however, but was very soon extended to classes containing elements other than carbon. A commencement was made in 1869, when Korner suggested 90 A SHORT HISTORY OF CHEMISTRY a structure for pyridine on lines analogous to Kekul^'s benzene formula : — H /'C\ H— C C— H I II H— C C— H Many other ring-systems, both carbocyclic x and heterocyclic, have since been brought into the scheme, and it will probably be simplest to draw up a series of lists illustrating the chief applications of Kekule's theory to other ring-systems. 1 The following terms are now used to define the various classes of organic compounds : aliphatic, derived ultimately from the paraffin hydro- carbons ; aromatic, from the benzene hydrocarbons ; carbocyclic (homo- cyclic), possessing a closed chain of carbon atoms; heterocyclic, a closed chain including other elements as well as carbon ; homocatenic, an open chain of carbon atoms; heterocatenic, an open chain of carbon and other atoms ; alicyclic, a fully saturated carbon ring-system (polymethylenes). THE HISTORY OF ORGANIC CHEMISTRY 91 (a) HETEROCYCLIC RINGS ANALOGOUS TO BENZENE. Proof of Struc- Isolation, ture. 1869 Korner 1846 Anderson ; in bone- oil. f 1871 Dewar 1842 Gerhardt ; from 1 1878 Grabe quinine and cinchona. 1883 Riedel 1871 Grabe and H. Caro ; synthesized from diphenylamine. 1875 Perkin 1875 Perkin's synthesis. (Collie, 1899) 1884 Ost. 1881 Merz and 1895 and ff. Occur Weith in nature as dyes. Kostanecki; synthe- 1869 Baeyer and 1866 Baeyer ; reduction Emmerling of indigo. 1873 Grabe 1872 Grabe ; in crude anthracene. 9* A SHORT HISTORY OF CHEMISTRY § E T!<6 'i ill ^ >•:-.. O M o oo co t^ r^-oo oo CN 1 t^ o> 00 00 oo oo h O "i. •= s *— XT *U .32 U 1) C 1) I 1) S PO oo 00 a CO o c u t^ 00 § «J II 1 0> r-> 00 C^ •^ HH "7^ ITI ^T1 i W KK HM ^ U DO U - II II II II E 4 E EE -v O — OO — O i «^ .s u — ^ rS •§ ^ « « • g 0 OJ 1 3 f 'Ja *o 1 rt E o N N C 2 ''rt 1882 Freund. CHa/ OH.,— CH2 1894 W. H. Perkin, jun. Cyclo-butane, tetramethylene | (only the chloro- oxy- and CH2— CH2 amido-tetramethylenes). CHa 1907 Cyclobutane : /\ Willstatter & Bruce. Cyclo-pentane, pentamethylene CH2 CH2 1893 J. Wislicenus. CHa— CHa CH2 /\ CH2 CH2 Cyclo-hexane, hexamethylene I 1894 Baeyer. CH2 CH2 CH, /CH2— CH.,— CH2 Cyclo-heptane, heptamethylene CH2Q | 1893 Markownikow. \CH2— CH2— CH2 (Cyclo-octane) cyclo-octadiene 1903 Ciamician and Silber. Cyclo-octane CH2— CH«— CH2— CH2 1907 Willstatter and Vera- CH2— CH2— CH2— CH2 guth. /CH2— CH2 — CH2 — CH2 Cyclo-nonane CH2<; 1907 Zelinsky. \CH2— CH2— CH2— CH2 Returning to the discussion of a formula for benzene, upon ' which all the other ring-formulae may be said to depend, it will THE HISTORY OF ORGANIC CHEMISTRY 95 be obvious that a considerable amount of laborious confirmatory work was necessary in order to prove beyond all doubt that benzene really possessed the structure assigned to it by Kekule'. This has been conscientiously carried out by a number of workers at different periods, and its nature will best be grasped by discussing it in the order of the problems which presented themselves for solution. (a) The formula postulates a perfectly symmetrical structure for benzene. This, or in other words, the equivalence of the hydrogen atoms in benzene has been proved by Ladenburg (1874), Wroblewski (1872-8), and others by replacing all the different hydrogen atoms in turn by the same group, the same product being invariably obtained. (b) It demands the presence of a closed chain of carbon atoms. The proof of the ring-structure was really completed by W. H. Perkin, jun. (1891-4) when he synthesized various derivatives of hexahydrobenzene as well as the hydrocarbon itself, and obtained products identical with those obtained by reduction of the benzene molecule (Baeyer, 1887-92). (c) It suggests the existence of one mono-substitution-pro- duct, three J di- and three tri-substitution products of benzene by one kind of group. This problem, "orientation," was one of the most troublesome to solve, and some years elapsed before definite proof was forthcoming that the theory was here in full accordance with the facts. The main factors contributing to the final satisfactory proof were as follows : — 1871. Baeyer showed that phthalic acid (from naphthalene by oxidation) is ortho-(i, 2)-dicarboxyl-benzene, and that isophthalic acid (from iso- xylene, produced in turn from mesitylene) is meta- (i, 3)-dicarboxyl-benzene, so that terephalic acid must be the/ara-(i, 4)-compound. 1874. Korner showed that an or^Ao-di-substitution product should yield two, a meta- three, and a^ara- only one tri-substitution product, and on this basis determined the orientation of the three known dibromobenzenes. 1 Excluding the possible second diortho-substituted substances, referred to later. 96 A SHORT HISTORY OF CHEMISTRY 1872. Griess proved that of the six known diamino-benzoic acids, two gave one diamino body, three gave another, and one another. Arguing conversely to Korner, he arrived at the same conclusion respecting the orientation of the di-substitution products. 1875. Ladenburg, by a complicated process, gave definite evidence that nresitylene was i, 3, 5 trimethylbenzene, thereby confirming Baeyer's de- ductions regarding isophthalic acid. These combined proofs put the practical utility of Kekule's theory beyond all doubt, but there has always been one uncer- tain point with reference to it, namely, the disposal of the fourth valency of each combination. Kekule represented these as forming three pairs of ethylenic bonds, but the stability and general chemical behaviour of aromatic derivatives are entirely opposed to such an accumulation of ordinary fatty " unsaturated Unkings". Between 1887 and 1892 Baeyer carried out an enormous series of experiments on the reduction of various car- boxylic acids of benzene, with a view to clearing up this point, but, although numerous important observations were made in various directions, the main object of the inquiry was not attained. Another line of attack was the physical properties of benzene. We shall see in Chap. x. (p. 181) how the numerical values of various physical properties are sometimes adapted for showing the constitution of a substance. It is possible in this way to calculate different values for benzene according to different formulae which it may possess, and to compare these values with that found for a given property by experiment. This has been done by Schiff (1883) and Horstmann (1887) with mole- cular volume, by Briihl (1894) with refractive index, and by Thomsen (1880), and Stohmann (1893) with reference to heats of combustion of benzene and various derivatives, but the results are conflicting and do not all point to the same for- mula. A property which seems to shed a little more light on the problem is the absorption spectrum of benzene, studied by Baly and Collie, and by Hartley, and referred to again later in this paragraph. THE HISTORY OF ORGANIC CHEMISTRY 97 Numerous formulae have from time to time been proposed in order to account for the remaining valencies of the car- bon atoms. These can be divided into two classes, static and dynamic, according as the component atoms are conceived in a state of rest or motion. The "diagonal" formula was the first of the former type, and was suggested by Claus in 1867. It bears an apparent resemblance to the Arm- strong-Baeyer "centric" formula (1892), which supposes the extra valencies to be directed to the centre of the benzene nucleus, so as mutually to satisfy each other. (In 1869 Ladenburg put forward his "prism" formula, which was later refuted, chiefly owing to Baeyer's work on the reduced benzoic acids.) The Armstrong-Baeyer con- ception of the benzene molecule was extended by Bamberger to numerous six-membered rings, both carbo- and hetero -cyclic. He succeeded in explaining by its means certain characteristic reactions of " conjugated aromatic nuclei," such as those in the napthalene anthracene and series, especially showing why reduction products such as, e.g. 7 q"i"°ii™ O 98 A SHORT HISTORY OF CHEMISTRY CH2 XX CH (ar)-tetrahydro-a-naphthol CH ^ should behave as aromatic substances while those like CH, (ac)-tetrahydro-a-naphthol (/ sj Jen resemble the fatty series more nearly in chemical behaviour. No one believes at the present time that the atoms in any compound are at rest, i.e. always remain in the same relative positions, and, therefore, it is more interesting to review the attempts made to account for the constitution of benzene on dynamical grounds. Kekule himself saw that, in addition to the questionable existence of " double bonds " in benzene, his original formula involved the possibility of two ortho-di-substi- tution products if the substituting groups were not the same. He, therefore, suggested (in 1872) that the fourth valency oscillated between the carbon atoms, thus : — s\ / i ii ^ i Knorr, in 1894, owing to his experiments on methyl pyrazole (cf. § 5), assumed that the hydrogen atoms, rather than the carbon linkings, were in a state of oscillation.1 1 It may be remarked that in a few instances such isomeric diortho compounds have been obtained, e.g. two o-nitrotoluenes. The difference»s THE HISTORY OF ORGANIC CHEMISTRY 99 On the other hand, Thiele arrived at quite a different formula in 1899, based on his theory of "partial valencies" (chap, iv., p. 54). Starting from Kekule's formula, he obtained the new formula for benzene as follows : — ;M Her UGH CH The most comprehensive formula of benzene is that proposed by Collie in 1897. He assumes that each carbon atom is vibrating, and that consequently the relative positions of the atoms are always altering. In this way the molecule passes and repasses through a series of phases, isolated phases being represented, as a matter of fact, by formulae such as Kekule's and the centric arrangement. An interesting point is that in this system there are seven possible ways of making and break- ing the " linkings " of the carbon atoms during a complete vibration, and these may possibly give rise to the seven " ab- sorption bands " in the ultra-violet spectrum of benzene. It should be observed that Collie's formula is steric, i.e. it pictures other atoms as they are arranged in space, not simply as a plane projection of the spacial configuration. Other steric but static benzene formulae (all based upon van 't Hoff's conception of the carbon atom as acting at the centre of a regular tetrahedron, with its valencies directed to- wards the apices) had been previously put forward, notably by between the two forms are very slight, and lie entirely in physical proper- ties (Knoevenagel). The phenomenon has been termed " moto-isomer- ism ". ioo A SHORT HISTORY OF CHEMISTRY Baeyer (1888) and Vaubel (1891), whose attempts, however, do not satisfactorily account for the phenomena shown on reduc- tion of the benzene nucleus by hydrogen. Sachse (1890) represented the most stable and symmetrical grouping of the atoms by six tetrahedra superposed upon six faces of a regular octahedron, leaving two parallel faces vacant. Both Thiele and Briihl supported Sachse's view. The whole position may be summed up by saying that at present Collie's formula offers the most satisfactory theoretical explanation of the variety of experimental data, while for ordinary practical purposes Kekule's original " hexagon " still suffices. § 5. Dynamic Isomerism— The most interesting develop- ments of organic theory during recent years have centred round isomerism of one kind or another, and in the following para- graphs we shall deal with* the progress of our knowledge of the chief kinds of isomerides. Numerous substances are now known which react under different conditions as though they possessed different struc- tural formulae, in other words, as though the same sub- stance combined in itself the properties of two isomeric compounds. A notable early example was that of isatin CO CO . OH (labile) or C6H /\CO (stable) (Baeyer, N NH 1883) ; two years later Laar called attention to other instances (nitrosophenol, acetoacetic ester, etc.) and suggested for the phenomenon the name tautomerism. Isomerism of this type has probably been more discussed in the case of acetoacetic ester than of any other single substance. This body was discovered in 1863 by Geuther, who formulated it as CH3 . C(OH) : CH . COOC2H5, while Frankland believed it to be ketonic, CH8 . CO . CH2 . COOC2H6. THE HISTORY OF ORGANIC CHEMISTRY '- te Both the mechanism of its formation and its chemical properties have furnished difficulties ; the latter tend to show that it reacts sometimes in the hydroxylic and sometimes in the ketonic form. As these two forms are characteristic of the tauto- merism displayed by many compounds, a convenient nomen- clature was suggested for them by Briihl in 1893, viz. the enol- (hydroxylic) and kefo- (ketonic) forms. A historical survey of tautomerism must include an account of the chief tautomers discovered, of the methods applied in their investigation, and of the theories put forward to explain the mechanism of the changes involved. The chief examples of tautomeric substances so far known are included in the following summary ; those discovered before the advent of modern structural views were, needless to say, only realized to be desmotropic (to use an equivalent term coined by Jacobson in 1887) at a much later date. The summary may conveniently be divided into the two main kinds of tautomers : — (a) Substances reacting in two forms, but only isolable in one. (b) Substances reacting in two forms, both of which can be isolated. 102 A SHORT HISTORY OF CHEMISTRY I O O o °^J^ . rt t^OO OO 00 en ^3 C rt - S) •= b£0 <" ^ 13.8 ^ i 393 1 iJ N c ? g .0 3 o « oKS 8^ 2 O^Z^ -\_ 1 af i tf E o" w o o u — u E »\ =CJ u a oo •Sl o u 'S"S ^£ !l •3^ §* THE HISTORY OF ORGANIC CHEMISTRY 103 (b) Different Forms Isolated. Chief Worker. Tribenzoylmethane One enol and one keto 1893 Claisen. Mesityloxideoxalic ester „ 1896 Claisen. Phenylnitromethane Hydroxylic (acid) and non- 1896 Hantzsch. hydroxylic (^-acid) Formylphenylacetic ester One enol and one keto 1896 W. Wislicenus. Dibenzoylsuccinic ester Various di-keto, keto-enol 1896 Knorr. and di-enol forms Diacetylsuccinic ester Various di-keto, keto-enol 1896 Knorr. and di-enol forms Benzylidene diacetylacetone Various di-keto, keto-enol 1899 SchifT, and di-enol forms Camphor-quinone phenyl- Normal hydrazone and 1899 Betti. hydrazone oxy-azo forms Arguments based upon both chemical and physical properties have naturally been used in attacking the problem, but the bulk of those derived from chemical changes have been proved within the last ten or twenty years to be invalid, since the different reagents used were shown to have first produced a particular isomer, which then entered into the reaction. Thus some reagents furnish the keto-, others the enol-isomer ; some exert a ketonizing, others an enolizing, effect. For this reason, all acidic or alkaline reagents have been banned, and chemists have found very few suitable reagents for tautomeric investigation by chemical means; Schiff (1898) used benzalaniline, which unites with either enol- or keto-acetoacetic ester, yielding entirely different products. Phenyl isocyanate has been used to detect hydroxyl or amino groups in desmotropic compounds, and sometimes alcoholic ferric chloride will show the presence of an enol-form without disturbing the constitution of the isomer (W. Wislicenus, 1896). Study of the physical properties has naturally often proved much more successful; differences in the values of different forms of keto-enol isomers were found by W. H. Perkin, sen. (1892) for magnetic rotation, Traube (1896) for molecular volume, and Briihl (1899) for refractive and dispersive power. Hantzsch traced the change of acids (R.CH:NO.OH) OH io4 A SHORT HISTORY OF CHEMISTRY to pseudo-acids (R . CH2 . NO2), and of ammonium bases C«H5 C6H6 c x C H ^C H to \\f-ammonium bases C6H4v / xN\ I CH3 OH CH3 by electrical conductivity measurements in 1896, and in the same year Wislicenus followed the keto- ^ enol change by a colorimetric method based upon the intensity of colour furnished by a standard alcoholic ferric chloride solution. Similarly, solubility and melting-point curves have been studied by Lowry (1904), Knorr and others, while Hartley and others have examined the absorption spectra of tautomeric compounds. Another property which is especially delicate when it can be applied is alteration in optical activity or mutarotation, as Lowry has termed it ; he has applied the method to the isomerism of nitro- and bromo-camphor and of a- and y-glucose. The theories of tautomeric change are chiefly associated with the names of Butlerow (1877), Laar (1885), Knorr (1894-95), Lapworth (1902), and Lowry (1904). Laar held the pheno- menon to be due to the rapid oscillation of particular linkings in the molecule, his explanation being thus intramolecular. Knorr, on the other hand, considered the process to be intermolecular, molecules of either isomer being present, but continually chang- ing into the alternate form ; for instance, with methylpyrazole (1894) obtained from two isomeric phenyl methylpyrazoles :— /\ CH3.C N -*. CH3.C NH CH — CH CH = CH In other words, the hydrogen atom oscillates, rather than the double linkings. In 1899 he stated further that tautomers tend in general to form an equilibrium (" allelotropic ") mixture of THE HISTORY OF ORGANIC CHEMISTRY 105 constant composition, the examples where only one form is known being limiting cases of this rule. He had also, four years earlier, expressed the conviction that the isomerizing effects pro- duced by different reagents were really due to the action of ions, and in 1902 Lapworth removed various discrepancies which occur if ordinary acid or alkaline ions are assumed to produce the effect by suggesting the changes were essentially caused only by the action of organic ions. Lowry in 1904 introduced the term dynamic isomerism to embrace all the forms of isomerism previously classed as tauto- merism, desmotropism, etc. He showed that tautomeric changes could be treated mathematically by the law of mass action, just like ordinary chemical "reactions of the first order," the velocity constants for typical cases having been previously worked out by himself in 1899 (optical activity of camphor derivatives) and by Kiister (1895). He assumed, too, that the mechanism of the change was a catalytic action due to the presence of ions. Finally, in 1904-5, Baly and Desch put forward an explana- tion, different from any of the above. Since simple hydroxylic or ketonic substances show no "absorption band" in the ultra-violet spectrum, while keto-enolic dynamic isomers usually possess one, they considered that the alteration \C = O-> = C — OH is responsible for the production of the band, i.e. tautomerism phenomena are due to vibrations in the molecule caused by the constant structural alteration. § 6. Sterio Hindrance — A problem not unconnected with those reviewed in the two preceding sections is that known latterly as " steric hindrance ". From time to time exceptions have been found to reactions which generally take a well-defined course, and in many cases it has seemed probable that the cause of the anomaly is the near presence of other non-reacting groups in the molecule which, apparently, protect the reacting radicle from attack by reason of their bulk. Victor Meyer was 106 A SHORT HISTORY OF CHEMISTRY the main author of this theory of steric hindrance, which dates from about 1894. The chief examples noticed previous to his work are : — 1872 Hofmann Substituted anilines such as C6(CH3)5NH2, do not yield quaternary ammonium iodides of the type R . NR3I. 1883-84 ,, The nitrile group of certain highly substituted benzonitriles could not be saponified in the usual way. 1891-92 Claus Noticed that the di-ortho-substituted cyanides were especially hard to saponify, but that the nature of the substituent also modified the reaction. 1890 Pinner Ortho-substituted cyanides do not readily give imino- ethers R . C\ \OEt 1890 Kehrmann Ortho-substituted quinones do not readily give oximes. 1891 V. Meyer „ „ „ „ hydra- zones. V. Meyer was thus led to examine the rates of esterification of a long series of substituted benzoic acids, and found that while the reaction proceeded equally well on the whole when the silver salt of the acid was heated with ethyl iodide, yet by the usual hydrochloric acid method very varying results were obtained. These led to his " Esterification Law ". In the substituted benzoic acids, the presence in the ortho-position COOH -^ to the carboxyl group of a radicle of low molecu- lar weight retards esterification, while groups of higher molecular weight may altogether prevent it. In 1899 the extension of Meyer's researches to the substituted fatty acids was undertaken by Sudborough, showing that sub- stituents in the methylene group next to the carboxyl behave in the same manner as ortho-substituents in benzoic acid, whiv° in 1895 and 1897 Meyer and Kellas respectively showed th those esters which are formed with difficulty are also the hardes THE HISTORY OF ORGANIC CHEMISTRY 107 to hydrolyze, showing clearly the "protecting " influence of the adjacent radicle. Other instances of steric hindrance occur in Bischoff s inves- tigations as to the conditions which influence chain- formation in the malonic and aceto-acetic ester syntheses (i 880-8) ; Schryver (1899) showed that the sodium salts of ortho- and para-nitrophenols, and di-ortho-bromophenols do not give the general reaction with camphoric anhydride, forming aryl hydrogen camphorates. The fact that other influences besides the size of the molecule niiy sometimes partially or completely mask the hindering effect is shown by the rates of reaction of sodium hydrogen sulphite with various substituted ketones (Stewart, 1905), and by the sulphination of a series of phenolic ethers : — R . C6H4 . OEt -> R . C6H3(OEt)(S02H) -> [R . C6H3(OEt)]2SO -> [R . C6H3(OEt)]3S. OH . The stage to which the latter reaction proceeds is found to depend upon : — (a) The steric hindrance due to the presence of ortho-substi- tuents. (b) The directing influence of the alkoxyl (OEt) group (Smiles and Le Rossignol, 1908). § 7. Stereo-isomerism (a) Geometrical Isomerism— There are two other kinds of isomerism remaining, which have been explained by considerations of the arrangement of the groups in space about the central carbon atoms of the organic molecule. The first which will be discussed is that which manifests itself most markedly in chemical properties ; the second, which has been known for a much longer period than the first, is an isomerism embracing three (or four) isomers in each instance, which in general differ mainly in their effect upon upolarized light. In either case we must first recapitulate the t;, views adopted as to the nature of the carbon atom before the j development of the theories of geometrical and optical isomers can be understood. loS A SHORT HISTORY OF CHEMISTRY Kekule"s views of organic structure were based upon the quadrivalency of carbon ; the disposition of the valencies in space was not considered. As we have seen, his theories, espe- cially that dealing with benzenoid compounds, cleared up the constitution of multitudes of compounds, but still there re- mained cases of isomers which were unaccounted for, such as that existing between maleic and fumaric acids or between the four tartaric acids. Van 't Hoff set out in 1874 to try to solve the problem by obtaining an idea of the arrangement of the groups about a carbon atom. Starting from the known fact of the equivalence of the hydrogen atoms in methane he argued that the disposi- tion of groups must be either : — a c (a) A plane arrangement, such as X \ b d (l>) A space arrangement whereby the affinities would be inclined equally to one another and directed towards the carbon atom (the familiar tetrahedron). Since (a) involves isomerism H\C//C \C/^ of substances, e.g. j^X '\Q Q/ '\H such as is contrary to observed fact, the alternative (/;) must be taken. Le Bel introduced practically the same view of the carbon atom at the same time, but independently of van 't Hoff. According to this view the atoms of substances containing an ethylenic bond would be so arranged in space that the four re- maining groups would all lie in one plane, and as the double linking would prevent free rotation of the central carbon atoms, geometrical isomerism might be expected :— a cad \C = C<^ and ^)C = C<^ ; b d b c THE HISTORY OF ORGANIC CHEMISTRY 109 a a a b \C = cS and ^>C = C<^ , etc. b b b a During the next ten years J. Wislicenus examined many cases of such geometrical isomerism in ethylenic compounds and published his results, " Die raumliche Anordnung der Atome," in 1887. The isomers used were maleic and fumaric, crotonic and iso-crotonic, citraconic and mesaconic, oleic and elaidic acids, etc., stilbenes (CGH5 . CH : CH . C6H5), tolanedihalides (C6H5 . CX : CX . CCH5), and many others. In 1892 Baeyer introduced convenient terms for the two kinds of isomers, viz. : — b c b a Cis-compound. Trans-compound. In the preceding years he had prepared a series of similar isomers in the case of some of his reduced aromatic acids. The " configuration " (cis- or trans-) of the isomers was based by J. Wislicenus chiefly on the ability to yield anhydrides or cyclic compounds, and the formation from the correspond- ing acetylene derivative in the case of cis-compounds, while superior stability and characteristic physical properties served to point out the trans-compounds. Some other cases of geometrical isomerism must be briefly referred to : — (a) Stereo-isomeric Oximes, %> Cl N . OH. — In 1883 ^2 V. Meyer and Goldschmidt obtained two benzildioximes, C6H5 . C( : NOH) . C( : N . OH) . C6H5, and five years later V. Meyer and Auwers also prepared two benzilmonoximes, a third dioxime being added in 1889. Their explanation of i io A SHORT HISTORY OF CHEMISTRY the isomerism was soon seen to be faulty ; meanwhile Beck- mann had obtained two benzaldoximes, which he formulated as O (a) C6H5 CH = N . OH and (ft) / \ , a view which C6H5 . CH . NH was speedily disproved by Goldschmidt. In 1890 Hantzschand Werner put forward their theory, which is simply an extension of van 't Hoff's views to the — CH : N— system, based on the assumption that the three nitrogen valencies are directed to the apex of a regular tetrahedron, so that, for instance, R . CH : N . OH may be spacially represented as :— This represents the isomerism as similar to the . CH : CH . cases, and the chemi- cal and physical characteristics of the isomeric oximes quite agree with this view, while, further, the isomerism appears and vanishes in accordance with the theory. In cases where only one oxime is known it is assumed that one of the radicles has a pre-eminently strong attraction for the hydroxyl group. The configuration of these isomers (termed syn- and anti- by Hantzsch, previously to Baeyer's cis- and trans-} has been determined by : — (i) Ready conversion of one (the syn-) form to a nitrile by loss of H2O. (ii) The " Beckmann change," which takes place as follows in presence of PC16 or HC1 and H2SO4 :— a.C.6 /a.C.OHx a . CO I! (II I -* I N.OH \ N.b / NH.i; a. C.b /HO. C.b\ CO . b /HO.C.JK I I V a.N / HO.N \ a.N / NH.a. (iii) Patterson and McMillan (1908) have followed the con- THE HISTORY OF ORGANIC CHEMISTRY in version of labile into stable isomeric oximes dissolved in ethyl- tartrate by means of the varying rotating power of the solvent. QH6\ (b) Stereo-isomeric Benzhydroximic Ethers /C : N . OIL — These, observed by Lossen in 1872, have been explained by Werner (1892-6) on the Hantzsch- Werner hypothesis. (c] Stereo-isomeric Hydrazones (Hantzsch, 1890) and osazones (Anschiitz, 1895) have also been noticed. (d) Isomeric Diazo-compounds. — In 1863 Griess discovered the diazo-compounds and isolated potassium benzene diazo- tate, C6H5N2OK. In 1894 Schraube and Schmidt obtained a second potassium salt by using different experimental condi- tions. Hantzsch forthwith assumed the differences to be due to geometrical isomerism, viz. : — C6HB.N C6H6.N II and || KO . N N . OK. The previous formulae for diazo-bodies were Kekule's azo- formula, C6H5 . N : N . X (1867), and Blomstrand's diazonium C FT formula, 6X5>N • N (1875), an<^ to these two Bamberger referred the isomeric diazotates. There ensued a protracted controversy between Hantzsch and Bamberger, in the course of which other isomeric diazo bodies (diazosulphates and cyanides) were obtained. Finally, it was generally admitted that both views were prob- ably correct ; while the Blomstrand formula probably better expresses the constitution of the salts of strong acids, the isomerism of derivatives of weaker acids is to be explained upon a stereo- chemical basis. § 8. Stereo-isomerism : (£) Optical Isomerism — In 1815 Biot noticed that sugar solutions rotate the plane of polarized light, a phenomenon previously observed in quartz by Arago (1811). In 1819 he showed that a substance which is thus ii2 A SHORT HISTORY OF CHEMISTRY "optically active" in the liquid remains so in the gaseous state. In 1820 Herschel pointed out that it was enantiomorphous (quartz) crystals which deviated polarized light, and Pasteur, thirty years later, found that sodium ammonium tartrate crystals were also enantiomorphous (i.e. possessed forms which were mirror images of each other), the two kinds of crystals moreover yielding respectively dextro- and laevo-tartaric acids. Pasteur suggested that the mutual cause of the hemihedral crystals and of the optical activity lay in some asymmetry of the atomic structure. Finally, in 1873, J. Wislicenus showed that the isomerism of the lactic acids from flesh and from sour milk (cf. p. 77) also manifested itself by the optical activity of one form, and stated that the cause must be connected with the spacial disposal of the atoms. Then, in 1874, came the Le Bel-van 't Hoff theory of the spacial arrangement of atoms, which accounted for the exist- ence of more than one derivative of substances containing an " asymmetric carbon atom ". It may be said that all optically active compounds have been found to possess asymmetry of this nature, although the converse is not yet experimentally true in some cases. Such compounds have been known for so long and are so numerous that examples are superfluous. The number of isomers of a compound containing one asymmetric atom is in general three — a dextro-, laevo- and racemic isomer ; the two former are alike in all properties but rotating power, in which they are opposite ; the latter usually varies somewhat in physical properties from the optically active compounds. A fourth stereo-isomer of THE HISTORY OF ORGANIC CHEMISTRY 113 tartaric acid, meso-tartaric acid, was discovered by Pasteur and explained by van 't Hoff as a compound in which the rotation of one-half of the molecule was compensated by that of the other half. The justice of this view was proved in 1892 when E. Fischer reduced mucicacidCOOH[CH2OH]4COOH (another meso compound) to galactonic acid CH2OH[CH . OH]4COOH, which being no longer an internally-compensated, but rather an externally-compensated (racernic) molecule, was successfully split up into active isomers. The meso isomers possess well- marked physical differences from the other forms. The correctness of Kekule's benzene theory has often been tested by attempting to obtain optically active forms of the benzene molecule. Such experiments (Le Bel, 1882 ; Lewko- witsch, 1888 ; V. Meyer and Liihn, 1895) have always, by their failure, afforded good negative proof of Kekule's views. A curious anomaly found in optical activity is that known as the Walden inversion ; an active compound usually yields by chemical change a new active compound of the same general sign, but Walden (1895) found that^-malic acid yielded /-chloro- succinic acid with PC15, while the latter gave /-malic acid or i ^ *U C •1 •£ •j o > c ^k— I •rt N § ^2 c a, V C oooooocooooooo x do 00 »> H CTlOO ( ro rj-c oo oo •*> 73 jc I S* •^ ffiw S oo f? « « -° — > - iia ffi Srs, u u cJ HO)2(EON)BH93 COMPOUNDS IN ORGANIC CHEMISTRY 121 and in consequence of this the distinction between " simple " ethers and "compound" ethers (later called esters) was soon observed. We may recall at this point how Williamson (and, independently, Chancel) finally solved the problems of the con- stitution of ether and of its production by the sulphuric acid process, showing at the same time how " mixed " " simple " ethers of the type R — O — R1 could exist. The anaesthetic properties of ether were discovered by Jackson (1842). Mention may also be made of the class of phenolic ethers, of which anisol, C6H4OCH3 (discovered by Cahours, 1841), may be taken as typical. The discovery of some characteristic esters is recalled in the following table : — Ethyl acetate 1759 Lauroguais. ,, chlorcarbonate 1833 Durnas (phosgene and alcohol). Ethylene dichloride 1795 Four Dutch chemists (ethylene + C12). „ dibromide 1826 Balard (ethylene + Br2). ,, di-iodide 1821 Faraday (sunlight on ethylene + I2). Chloroform 1831 Liebig; Soubeiran, 1847, used in sur- gery (Simpson). lodoform 1832 Serullas. Ethyl hydrogen sulphate ( 1833-40 Hennel, Serullas, Magnus and and ethionic acids 1 Regnault. Ethyl hydrogen phosphate 1833 P£louze. „ „ carbonate 1840 Mitscherlich. Glyceryl trinitrate 1847 Sobrero (" nitro-glycerine "). (The products of the action of HNO, on ethyl alcohol were studied by Debus, 1856.) § 3- Oxygen Derivatives : (8) Carbonyl Compounds, Reactions of Condensation — Aldehydes and ketones have been prepared chiefly by the oxidation of alcohols (Scheele, 1774), the distillation of calcium salts of fatty acids (William- son), the action of zinc alkyls on acid chlorides (Freund, 1860), Gattermann's aluminium chloride reaction (cf. p. 118) and Grignard's reaction (1900; the action of magnesium alkyl halides on form-alkylanilides, formic ester, and iso-nitriles (aldehydes) and on nitriles and amides (ketones)). The 122 A SHORT HISTORY OF CHEMISTRY detection of the carbonyl group has been effected by hydroxy- lamine (oximes, V. Meyer, 1882) and phenylhydrazine (E. Fischer, 1877). The development of a series of "condensa- tion reactions " of aldehydes and ketones (reactions accom- panied by elimination of the elements of water or alcohol) may here be dealt with : — (a) The aldol condensation of aldehydes or ketones in presence of acid or alkali, e.g. CH3CHO + CH3 . CHO _> CH3 . CH(OH) . CH2 . CHO (aldol) -> CH3. CH : CH . CHO (crotonaldehyde). Wurtz (1872) studied this particular case, but in 1866 Baeyer had observed the similar forma- tion of mesityl oxide and phorone from acetone. (b) The benzoin condensation first noticed by Liebig and Wohler (1832) in the action of KCN on benzaldehyde, but only satisfactorily explained by Lapworth in 1903. (c) The Claisen condensation of carbonyl derivatives with substances containing the keten group — CH2 — CO — ; examples of compounds so formed are benzalacetone (Claisen, 1881) ; o-nitrobenzalacetone (Baeyer, 1882 ; used in indigo-synthesis), cinnamalacetone (Einhorn and Diehl, 1885), a-acrose (dl-fructose) (E. Fischer, 1887, from formaldehyde), and ionone (Tiemann, 1893, from citral). The historically noteworthy members of this group appear on the opposite page. § 4. Oxygen Derivatives : (c) Carboxylic Acids — The importance of this class for the determination of constitution and other problems is obviously very great, and consequently a very large number of syntheses have been devised ; we have only space to refer to a few, such as oxidation of alcohols or aldehydes, saponification of nitriles [Dumas and Frankland and Kolbe (1847), acetoacetic and malonic ester syntheses (cf. § 5), and metal-alkyi syntheses (Na + CO2 + C6H5Br, Kekule, 1866 ; finely-divided silver on halogen fatty acids, J. Wislicenus, 1868 ; zinc on chloracetic and oxalic esters, Fittig and Daimler, 1887 ; zinc on ketones and iodacetic esters, Reformatski, 1887, used in synthesis of citric acid, Lawrence, 1897) ; Grignard reaction]. Perkins' reaction for the preparation of ethylenic acids by heat- ing a mixture of aldehyde, sodium fatty acid salt and acid COMPOUNDS IN ORGANIC CHEMISTRY 123 c ex, 11 Q M ^0.15 r? M »-— - 03*00) c2-^ • 1 ?^k ll«l I CDl^-S 2 00 00 M H ••la >OU J 00 OO CO ro fO t^ ^ 00 00 00 00 00 00 00 5 c •8 J a n3r--2rt ~wEP T3« ? | Ijlj l»|l <| •> 10 me ce c n §5 ^ ^ • PC Ko oo 55 -^!|T'' o KM ! i §•§ 0 -hp-S^cx ^ ** is. Q i24 A SHORT HISTORY OF CHEMISTRY anhydride (1868, coumaric ; 1875, cinnamic acid) has been studied in addition by Baeyer, Conrad, Fittig, and others, but its precise mechanism is not quite definitely understood. In the course of his work Fittig was able to shed much light on the constitution of lactones (paraconic acids, 1894-1904), and to confirm the ideas put forward by Erlenmeyer, sen. (1880), to account for Saytzew's butyrolactone (1873) and Bredt's isocapro- lactone (1880). The structure of amido-acids (see also chap, viii.) was defined when Perkin and Duppa obtained glycocoll (already prepared from glue (Braconnot, 1820), hippuric acid (Dessaignes, 1846), and bile (Strecker, 1848)) by the action of ammonia on bromo- acetic acid in 1858, and that otoxy-acids followed, since glycocoll had been submitted to the action of nitrous acid (Strecker, 1848). The latter have also been prepared by the action of zinc alkyl halides on oxalic ester (Frankland and Duppa, 1865), from aldehyde cyanhydrins (Wislicenus, 1862) and from Grignard's reagent and ketonic esters (McKenzie, 1905). The first nitrites to be prepared seem to have been proprio- nitrile (1834, Pelouze, Ba(C2H5)SO4 + KCN), aceto-nitrile (1847, Dumas, phosphoric anhydride and ammonium acetate) and benzonitrile (1844, Fehling). With the anhydrides (Gerhardt, 1852) may be mentioned the acid peroxides (Brodie, 1864, from the former and BaO2). Various improvements have been made in the preparation of acid chlorides since Liebig and Wohler produced the first member in 1832 by the chlorination of benzaldehyde, such as the interaction of the sodium salts with phosphorus pentachloride (Cahours, 1846), trichloride (Bechamp, 1856), oxychloride (Gerhardt, 1851), or thionyl chloride (Hermann, 1883). Reference must finally be made to the amides, such as oxamide (from ammonium oxalate, Dumas, 1830 ; ammonia and oxalic ester, Liebig, 1834), benzamide (ammonia and benzoyl chloride, Liebig and Wohler, 1832), acetamide (Dumas, 1847) and the anilides (Gerhardt, 1845). Details of interest are connected with the following acids ; — COMPOUNDS IN ORGANIC CHEMISTRY 125 if!! S 8.-S 8 a 2^ 2^ o o •5 a IU] 03 . C C N *— * .2 o N 3 *— ' u 5«lx ala^i .*• C III lU C c/3 §<§« 41 1 ? a it! -u m^" g g.«fjg '^ . 3 IS — -^ §g|«'iS'S«t&-»8®':3 . iJS'-S E «z '3 8 SI'S 2.SP»a sfiJJ .9'Sj^P « — o § ^§-5 « g 8.S^^ g..5f , hn )vi !>' 0) tL. tn-« — yi>C_Q»-^*r; TSUjH-!»' o5rS_Q N_. ,Soi3rtr>PcS_^4JlU;i_£5 Sc2o -*t o ^ Si 3*J ^!5 -IIP 8 § • 1! § sfJufsT ffl % ffi dr drjr dr udr o o If1 II ! ! &•§ ^^ 126 A SHORT HISTORY OF CHEMISTRY § 5- Oxygen Derivatives : (d) Ketonic Acids — This sec- tion of the organic acids is particularly important, because many of its members (all those possessing the group — CH., - CO — ) are able, by virtue of the acidic properties of the methylene hydrogen atoms, to enter into all manner of complex synthetic reactions. The following are typical : — (a) Action of chlorcarbonic esters on the sodium compounds of aceto- acetic ester, malonic ester, etc. (1877 Conrad; 1882-6 Bischoff; in 1879 Conrad undertook a comprehensive investigation of the malonic ester syntheses, foreshadowed by van 't Hoff in 1874). (b) Action of iodine on the sodium compounds (dioxysuccinic esters, Bischoff, 1884). (c) Action of alkylene bromides on the sodium compounds (Bischoff, 1 880-8 ; Perkin, jun., 1902). (d) Condensation of phenanthraquinone and acetoacetic ester by ammonia (Japp and Streatfield, 1883). (c) Condensation of aldehydes and acetoacetic ester by organic bases (Knoevenagel's reaction, 1893). (/) Condensation of olefinic or acetylenic esters with sodium compounds of acetoacetic, malonic, or cyanoacetic esters (Michael's reaction, 1887). (g) Condensation of hydrazines, etc., and ketonic esters, yielding hetero- cyclic bodies (cf. § 8). The parent member of the polyketides> as Collie (1907) has proposed to term substances containing the — CH2 . CO — group, is keten CH2 : CO, isolated by Wilsmore and Stewart (1907) ; substituted ketens have been prepared by Staudinger from bromacyl bromides and zinc, while a new oxide of carbon, carbon suboxide C3O2, prepared by distilling malonic ester and phosphoric anhydride (1906, Diels and Wolf), appears to be a keten derivative, CO : C : CO. Acetylketen is a polymer of keten, and an internal anhydride of acetoacetic acid (Chick and Wilsmore, 1908). Typical ketonic acids are : — CH3.CO.COOH Pyruvic; obtained by iatro-chemists in distilling " tartar," and by Berzelius (1835). CH3CO . CH2 . COOH Acetoacetic (referred to in chap. vi.). CH3CO . CH2 . CH2 . COOH Laevulinic ; 1874 v. Grote and Tollens. COMPOUNDS IN ORGANIC CHEMISTRY 127 CO(CH2 . COOH)2 Acetonedicarboxylic ; 1884 v. Pechmann (from citric acid). C6H5. CO . CHa . COOH Benzoylacetic : 1884 Perkin (phenyl-propiolic and strong sulphuric acid) ; 1887 Claisen (condensation of benzoic and acetic esters). § 6. Nitrogen Derivatives — These have been very fully studied during the past century, since the constitution of so many vegetable and animal products, as well as the preparation of dyes, explosives and other technically valuable substances depends on the function of the nitrogen-containing group. Commencing with nitro-compounds (the first of which, ex- cluding picric acid, was nitrobenzene, Mitscherlich, 1834), we notice the evolution of methods of nitration in the aromatic series, and the preparation of the first aliphatic members by Kolbe and by V. Meyer in 1872. The latter extended his studies to the conversion of nitre-paraffins to nitrols, nitrolic acids, etc. Nitroso compounds were obtained by the action of mercury diphenyl and nitrosyl bromide (Baeyer, 1874), and of nitrous acid on secondary amines and on phenols (Baeyer and H. Caro, 1874, 1874). The flw/dfo-derivatives form the most important class of nitrogen compounds. Aliphatic amines have been prepared by intraction of alkyl isocyanates and caustic potash (Wurtz, 1848), alkylation of ammonia (Hofmann, 1849), reduction of nitriles (Mendius, 1862), and hydrolysis of isonitriles (Hof- mann, 1868); Hofmann (1885) also illustrated the conversion of amides (by bromine and potash) to the next lower amine. Besides Hofmann's alkylation of aniline, aromatic amines have been prepared by reduction of nitro-compounds by ammonium sulphide (Zinin, 1841), hydrochloric acid and zinc (Hofmann, 1845), iron (Bechamp, 1852) or tin (Roussin), and electrolytic- ally (Lob, 1900). The electrolytic reduction of nitrobenzene, in particular, has led under suitable conditions to methods for the preparation of azoxy-, azo-, hydrazo-, or amino-benzene. The following individual amines and related derivatives are worthy of note : — 128 A SHORT HISTORY OF CHEMISTRY Aniline (1826 Unverdorben, distillation of indigo ; 1834 Runge, " cyanol " in coal-tar ; 1841 Fritzsche, " aniline," from indigo and potash ; 1841 Zinin, reduction of nitrobenzene — all four substances proved identical by Hofmann, 1843) ; p-toluidine (1845, Hofmann) ; diphenylamine (1864, Hofmann, from rosaniline) ; azoxybenzene (Mitscherlich, 1834) ; hydrazo- benzene (Hofmann, 1863), which changes so readily to the isomeric ben- zidine (already obtained by Zinin in 1845 by acid reduction of azo-benzene, the intermediate hydrazo-compound being overlooked) ; and a- and /3- naphthylamines (Zinin, 1842; Liebermann, 1876). The constitution of the numerous intermediate reduction products of nitrobenzene is mainly due to Erlenmeyer and Kekule*. The derivatives of hydrazine belong here and include phenyl- hydrazine (E. Fischer, 1875, who obtained it from potassium phenylhydrazine sulphonate, previously prepared by Strecker in 1871), and the alkylhydrazines (E. Fischer, 1879). Other amino-compounds are : — CO(NH2)2 Carbamide 1773 Rouelle (in urine) ; 1828 Wohler (from ammonium cyanate). C(NH)(NHa)., Guanidine 1861 Strecker (oxidation of guanine). CN . NH2 Cyanamide 1838 Bineau (CNC1 + NH3); recently intro- duced as a manure. The first diazo-compounds were obtained by Griess in 1863 from aniline; the problem of their constitution has already been discussed (ch. vi. § 7). The discovery of diazo-amido- benzene and its conversion to amido-azobenzene (Griess, 1862) was of great importance to the dyeing industry. Other in- teresting diazo-bodies are : — /N C6H5.N^ Diazoimidobenzene 1866 Griess. ^ || Di CH3 Diazomethane CO2C3H5 . CHN2 Diazoacetic ester 1883 Curtius (nitrous acid and glycocoll). CH3 . N = N . NH . R Aliphatic diazo-/igo7 Dimroth (Grignard reagent amido compounds \ and diazo-paraffins). There remain, in conclusion, the isonitriles (predicted by Kolbe, and discovered at about the same time by Gautier COMPOUNDS IN ORGANIC CHEMISTRY 129 (alkyl iodides and silver nitrate) and Hofmann (chloroform, primary amine, and alkali) in 1866), and the isonitroso com- pounds, including the oximes (Victor Meyer, 1883 and the compounds formed by the action of nitrous acid (or amyl nitrite) on the methylene group — CH2 — - under suitable con- ditions (V. Meyer, 1882). Other nitrogenous compounds will be mentioned in cort^ nexion with the history of alkaloids, proteins, dyestuffs, etc* § 7. Derivatives of Elements other than Oxygen or Nitrogen — The researches in this direction group themselves into three main classes : — (a) The study of compounds analogous to the amines. (b) The study of sulphur compounds. (c) The study of " organo- metallic " derivatives. (a) To this section belongs the work on the alkyl derivatives of phospho- rus, arsenic, and antimony. Aliphatic tertiary phosphines were discovered by The'nard in 1846 (from alkyl iodides and calcium phosphide), while Hof- mann prepared the primary and secondary bases by his alkylation method in 1871. Aromatic phosphines (C6H5PH3, C6H5PO2 and C6H5P : PC6H5) were derived by Michael in 1876 from C6H5PC12. Tertiary and quater- nary arsenic and antimony compounds have been chiefly studied by Lowig and Landolt (1853) ; the primary and secondary arsenic derivatives were found to be non-basic, the primary (mono-methyl) bodies being due to Baeyer (1858). The secondary compounds are of especial interest, for they form one of the three " pillars " of the older radical theory, and were studied much earlier than any of the others. They were investigated by Bunsen (1837-43), who isolated many derivatives of " cacodyl " (CH3)aAs — from " Cadet's fuming arsenical liquid," first prepared in 1760 by Cadet by distilling arsenious acid and potassium acetate. (b) Organic sulphur compounds have been found to contain bi-,quadri-, or sexa-valent sulphur, and while the bi- and sexa-valent compounds are now well defined there is still room for improvement in our knowledge of the behaviour of many substances containing quadrivalent sulphur. The bi-valent derivatives include the mercaptans and sulphides (C3H5SH, discovered by Zeise, 1834; (C3H5)2S, allyl sulphide, isolated from garlic by Wertheim, 1844 ; C6H5SH, Kekule, 1867) ; derivatives of thiocarbonic acid (CS2, Lampadius, 1796, from pyrites and coal; COS, v. Than, 1867; xanthates RO.CS.SK, Zeise, 1824, from CS2, alcohol and soda); CS(NH2)3 thiourea, Reynolds (1869, from NH4CNS) ; thioacetic acid 9 130 A SHORT HISTORY OF CHEMISTRY CH3 . COSH, Kekule, 1854 5 ancl the mustard oils (alkyl isothiocya nates, R . N : C : S) of which allyl isothiocyanate (in mustard seeds) was the first to be isolated (Bussy, 1840), and whose constitution and synthesis were worked out by Hofrriann about 1868. The most interesting quadrivalent sulphur compounds are the sulphinic acids (aliphatic, 1857, Hobson ; aromatic, 1862, Kalle), sulphoxides (1866, Saytzew) and sulphonium bases (aliphatic, 1865, Cahours ; aromatic, Smiles and Le Rossignol, 1906). Thionyl derivatives of amines, R . N : SO, have been studied by Michael (1891). It is probable that the constitu- tion of not a few dyestuffs containing sulphur will be shown to depend upon the presence of quadrivalent sulphur. The sexavalent derivatives are perhaps the best known, such as the tmlphonic acids (methylsulphonic, Kolbe, 1845, benzene sulphonic, Mits- cherlich, 1833 ; sulphanilic (p-aminobenzenesulphonic), Gerhardt, 1845 (sul- phonation of aniline) ; and the many dyes which are used in the form of sulphonic acids for the sake of superior solubility), and the sulphones (Saytzew, 1867 ; a-disulphones R . SO2 . SO,R, Kohler and Macdonald, 1899, and Hilditch, 1908; sulphonal (CH3)2C(SO2C2H5)2 discovered by Baumann (1888), and applied as a soporific by Kast (1889) ; saccharin . >so'\ C6H4 <^ /NH, discovered by Remsen and Fahlberg (1879) in the XCO/ alkaline oxidation of o-toluene sulphonamide). (c) The organic compounds of silicon have proved interesting since Wohler in 1863 showed their close analogy to the corresponding carbon derivatives, and the chief workers have been, for the aliphatic compounds, Frankland (zinc alkyls and SiCl4) and Friedel and Crafts (1863) ; for aro- matic derivatives, Ladenburg (C6H5SiCl3, 1874) and Polis ((C6H5)4Si, 1886). Kipping has recently prepared many new silicon derivatives by the action of different magnesium alkyl iodides on silicon tetrachloride (1907). Alkyl compounds of other metals followed chiefly upon Frankland's discovery of zinc ethyl in 1849, and were prepared from the zinc alkyls and metal chlorides, e.g. tin (Lowig, 1852, Cahours, 1860) ; lead (Pb(C2H5)4, Buckton, 1859). Mercury alkyls were made from sodium amalgam and the alkyl iodides (Frankland, 1864 ; Hg(C6H5)2, Otto and Dreher, 1870). The zinc alkyls are exceedingly difficult to manipulate, and Fleck (1893) found the magnesium compounds even worse ; Barbier, however, found that a mixture of finely-divided magnesium and methyl iodide acted readily and with the same result as the alkyl derivative (1899), and in 1900 Grignard made an extensive study of the reaction between magnesium and alkyl \ halides, showing how the compounds formed ( Mgf J could be used COMPOUNDS INORGANIC CHEMISTRY 131 in all manner of syntheses (Grignard's reagent). Pfeiffer has applied the reagent to various metallic chlorides and has obtained in this way alkyl derivatives of mercury, thallium, bismuth, platinum and other metals. § 8. Heterocyclic Compounds — Dozens of ring-systems consisting of carbon, oxygen, sulphur and nitrogen atoms have been synthesized within the last forty years, and historical data of the chief members of these have already been furnished (chap. vi. p. 91) ; it remains to give some idea at this point of the manner in which the methods of synthesis of the various types have developed, and we may confine our attention to the five- and six-membered rings, the rest being relatively unim- portant. The synthetic reactions may be grouped as follows : — I. Pyrogemtic reactions : — Carbazole | j (Grabe, 1873; from diphenylamine). NH S Thiodiphenylamine [Til (Bernthsen, 1888 ; diphenylamine and sulphur). .N— C. Pyrimidines C X NH :C (E. v. Meyer, 1889 ; polymerization of nitriles) ^N— CT II. Reduction reactions : — CH Indol | | CH (Baeyer, 1869; from o-nitrocinnamic aldehyde). \x NH CH ,/\ Indazoles j j NH (Nolting, 1890; from o-nitro compounds) \/ N 132 A SHORT HISTORY OF CHEMISTRY N /\x\ Benzimidazoles | | CH (Hobrecker, 1872 ; from o-nitro compounds). NH O Benzoxazoles | j CH (Hubner, 1881 ; from benzoyl-y-nitrophenols). Quinoxalines (Hinsberg, 1896 ; from tf-nitrophenyl-a-amido-acids). N III. Oxidation reactions : — N Phenazines i886; from o-diamines and a-naphthol). N Quinolines | | | (Skraup, 1880 ; from anilines and glycerol). N IV. Condensation reactions (a) from a.-diketones : — C=C \ Glyoxalines I r//N (Rodziszewski, 1882 ; with ammonia and aldehydes). Dihydropyrazines (Weil, 1900 ; with alkylene diamines). CH2\/CH N N Quinoxaline I (Hinsberg, 1887 ; with o-diamines). COMPOUNDS IN ORGANIC CHEMISTRY 133 (b) from ft-diketones : — x\ Pyridines | | (Hantzsch, 1882 ; with aldehyde ammonia). N /\/ \ Quinolines | j | (Knorr, 1886 ; anilides of /3-keto-acids). N c/\c Pyrimidines (Pinner, 1893 ; with acid amidines). N\/N C Coumarones ( | | (Hantzsch, 1886 ; chloroacetoacetic ester and phenates). O (c) from y-diketones : — Furfuranes \/ O (Paal, 1885; elimination of water). I I Thiophenes j j (Paal, 1885 ; with phosphorus pentasulphide). \x s I I Pyrrols | | (Paal, 1885 ; with ammonia). V X NH I I Thiophenes | | (Volhard and Erdmann, 1885 ; sodium succinate and PaS,). \x S (d) from o-diamines : — N \/\ /\/\ Benzimidazoles | CH (Ladenburg, 1875 ; with fatty acids). \ /\ / NH 134 A SHORT HISTORY OF CHEMISTRY N Quinoxaline | j (Hinsberg, 1887 ; with cyanogen). N N Phenazine | | (Hinsberg, 1896 ; with o-quinones or pyro-catechol). (e) from o-aminophenols : — O Benzoxazoles Phenoxazine C . R (Ladenburg, 1877 ; with fatty acids), I I (Bernthsen, 1887 ; with pyrocatechol). \/\/ (/) from amino-aldehydes or ketones : — N =CHx Oxazoles I )O (Blumlein, 1884 ; ct-chlorketones and amides). HC— CH/ Pyridine | J (Schiff, 1861 ; aldehyde-ammonia and aldehydes). V Quinoline | Pyrazine N (Friedlander, 1883 ; o-aminobenzaldehydes and— CH2. CO— compounds). (Skraup, 1893 ; aminoaldehydes and aminoketones). N (g) from ammo-acids ; — Pyridine | ( (Bottinger, 1881 ; from gl utaconamic acid). COMPOUNDS IN ORGANIC CHEMISTRY 135 Acridine I | | | (Bernthsen, 1884 ; from diphenylamine and acids). N (/i) from hydrazine and hydroxylamine : — Indol I | (E. Fischer, 1886 ; from certain phenylhydrazones). \/\x NH Pyrazoles | /NH (Claisen, 1888 ; hydrazines and j8-diketones). HC = N / Pyrazolones CO^ | (Knorr, 1883 ; phenylhydrazjne and )8-ketonic esters). CH Indazoles | I NH (Fischer and Tafel, 1885; from o-hydrazine cinna- mic acids). N Triazoles | )NH (Andreocci, 1892; acid hydrazides and amides). Isoquinoline (Bamberger, 1894 ; from cinnamaldoxime). \/\/N (/) Per kin s reaction : — Coumarin (a-Pyrone) | | | (Perkin, 1865 ; from salicylaldehyde and acetic \/\/CO anhydride). O (/) Alkaline condensation or decomposition : — Coumarone | | | (Fittig, 1883 ; from coumarin (loss of CO) ). O CO Isatin I | CO (Baeyer, 1880; alkalies on o-nitrophenylpropiolic acid). \/\/ NH 136 A SHORT HISTORY OF CHEMISTRY Other points of interest which may be chosen from the history of the heterocyclic group are : — (a) The furfurane, thiophene and pyrrol compounds, which present so close an analogy to the benzene and pyridine de- rivatives in many ways, although this relation and the cognate relationships of coumarone, indol, carbazole, etc., to the three first-named bodies were not generally recognized till about 1885. (b) The connexion found to exist between a large number of natural products, notably certain vegetable dyes (quercetin , fisetin, etc.), and the y-pyrone compounds CO /\ pyrone || <||, benzopyrone | | and \/ \, c xanthone | which have been the subject of study by Kostanecki, A. G. Perkin, and others of recent years. (c) The importance of many derivatives of pyridine, quinoline and ispquinoline (especially the carboxylic acids) for the deter- mination of the constitution of the alkaloids, most of which yield on rupture of their complicated molecules one or more of these simple decomposition-products. CHAPTER VIII THE CHEMISTRY OF PLANT AND ANIMAL LIFE § i. Chemical Processes in the Vegetable and Animal Kingdoms — Although many of the alchemists professed to regard their science as being, by reason of its connexion with the process of life, too sacred and mysterious for the average person to understand, there came a time when botanists and physiologists were inclined to disparage the utility of any chemical explanation of vital processes, holding that these were caused by a " vital force " of a nature entirely different to the ordinary inorganic "chemical affinity". In spite of all the chemical work, such as Lavoisier's analyses of typical organic bodies and Wohler's or Kolbe's syntheses of organic from in- organic materials tending to prove that there was nothing chemi- cally anomalous about an organic compound, this opinion held general sway until about the middle of the nineteenth century. Perhaps it is partly in consequence of this that the first modern investigations on the chemical reactions going on in plant or animal life were undertaken in most cases by chemists rather than physiologists. In this way Fourcroy, Vauquelin, and later, Berzelius, studied animal chemistry, while Senebier, Dutro- chet and especially Saussure worked out the conditions under which carbonic acid is absorbed and the carbon assimilated by plants, noting that certain parts of plants evolve instead of ab- sorbing the gas and that a small evolution of heat also takes place, thus forming an analogy with animal breathing. One of the important problems in both plant and animal realms is nutrition, and the chemical nature of the subject be- 138 A SHORT HISTORY OF CHEMISTRY came plain through the researches just mentioned and especi- ally by the work of Liebig, who embodied his results in a pamphlet published about 1842. With reference to animal nutrition, he stated that it was based upon a series of chemical reactions and distinguished between real nutrients and sub- stances which effect animal change but do not build up the tissues; he disproved the theory (which at that time had held sway for about a century) that plants are nourished by a certain "humus" in the soil, and showed that in reality they live on water, carbonic acid, ammonia, nitric acid, silica, and in lesser degree elements such as phosphorus, sulphur, magnesium, calcium, iron, potassium, which are built up into complex com- pounds in the vegetable cells. This work is of course the foundation of scientific agriculture, which consists in supplying to a crop the correct amount of the constituents needful for its particular development. Very much work has been done since Liebig's time on the composition of soils, and agricultural chemistry is to-day a science in itself, special laboratories being scattered over Europe and some of the British colonies for the investigation of plant-chemistry and the guidance of the farmer. At the same, time the selection of human food has been based upon more scientific ground owing to the work of Liebig Pettenkofer, Voit, and many others, while the importance of controlling its quality is now generally recognized, as evidenced by the numerous official analysts engaged in the work and the recent creation (1908) of an annual international congress to advise upon legislation respecting matters of food and hygiene. Moreover, the rapid extension of structural knowledge in organic chemistry has encouraged the isolation of many of the complicated substances occurring in living things with a view to elucidating their constitution. Thus chlorophyll, the colouring matter of leaves, has been repeatedly studied (Sachs, Pringsheim, etc.), and has quite recently been obtained in a crystalline state by Willstatter. Similarly blood (with its components haemo- CHEMISTRY OF PLANT AND ANIMAL LIFE 139 globin, hsematin, etc.) has frequently received attention (Magnus, Meyer, etc. etc.), and so have other organs and products of the animal metabolism such as flesh (Liebig, Strecker, Helmholtz, Briicke), fats and milk (Chevreul), saliva (Leuchs discovered the enzyme ptyalin^ 1831 ; Ludwig, Briicke), gastric juice (Kiihne), and urine (Liebig and Voit estimated urea ; Wohler and Dessaignes showed formation of hippuric acid ; etc.), the names simply indicating one or two of the foremost workers. Side by side with the efforts to ascertain the structure of vegetable and animal products such as the alkaloids, or sugars, numerous attempts have been made to produce them by synthesis, and in not a few cases these have been attended with success. Nevertheless it has often been remarked that such syntheses resemble the natural process in little more than the identity of the end-product, for plants and animals only have recourse to agents such as phosphorus pentoxide or pentachloride, potassium cyanide, caustic soda, or strong sulphuric acid (to name a few of the favourite synthetic laboratory reagents) under the most abnormal and dismal conditions. We cannot unfortunately trace the interesting story of bio- logical chemistry in further detail, but must confine ourselves to a description of the chemical development of four important classes of naturally occurring organic products, viz. the alkaloids, the terpenes, the sugars and other "carbohydrates," and the purines, proteins and allied nitrogenous substances. § 2. The Alkaloids — The presence of crystalline basic sub- stances in certain plant-juices was not recognized until rather more than a century ago, when Seguin prepared " morphium " from opium (1803). "Morphium" was soon found to be a mixture of several bases, from which one, morphine, was isolated in the pure state by Sertuerner in 1817. Other allied bodies such as strychnine, quinine, coniine were rapidly discovered and the generic name of alkaloids was given to them on account of their basic properties. Later on, Liebig showed that the latter was due to the nitrogen present in all the compounds concerned, 140 A SHORT HISTORY OF CHEMISTRY and much more recently, when the constitutions of the funda- mental types of organic compounds had been worked out, it was found that most alkaloids could be broken down by more or less violent means into simpler bodies, allied to pyridine (Konigs, Ladenburg, Weidel). In consequence of this and of the pre- paration of artificial complex pyridine bases, the term alkaloid is now generally considered to embrace all basic complex derivatives of pyridine or other heterocyclic nitrogenous ring- system. Most of the alkaloids have marked therapeutic (toxic or anaesthetic) properties and considerable attention has therefore been paid to their detection by a variety of reagents, such as double metal halides (Pettenkofer, 1844), phosphomolybdic acid (Sonnenschein, 1856), polyiodides (Jorgensen, 1870), or hydro- ferrocyanic acid (E. Fischer, 1877). So various have been the methods for determining alkaloid structure and attempting alkaloid synthesis that it is impossible to name them here ; we can only give a summary (p. 141) of the chief men connected with the more important alkaloids (with the approximate date of their work) and mention that the most prominent workers in this have been Pelletier and Caventou (1829), Liebig (1835), Regnault (1840), Laurent (1845), Ander- son (1850), Ladenburg (1870-), Skraup (1880), Freund, Pschorr, Knorr, Willstatter (1890-), A. Pictet (1895-). § 3. The Terpenes — The chemical history of the " essential oils " formed by many plants and trees falls naturally into three divisions : — (i) A preliminary period, in which crude essences were ex- tracted from the plants, chiefly for their perfume ; this extends to the remotest times, for the ancients knew how to make terpentine oil as well as oils of olive, almond, pear, etc. (most of which have been already dealt with). The alchemists added numerous others, such as those from rosemary, thyme, etc., and the group of herbal essences has continued to multiply steadily. CHEMISTRY OF PLANT AND ANIMAL LIFE 141 '§ S I a |i Pn-S 1 S SP S I ^ ^ 3 •S *3 •£ c* "3 S a - *1 | « w ! i - w . 11* I § •S I c o s g pq 3 ^ ^SlllMSl B? u SSS| 0 6 ' S > '-S > 'S > '-S > ^ a; *o O M 00 O> O> ^ ^O N N H M H N oo 00 00 00 00 OO 00 ^ H M M M M M H o o iO "*"* S lO'— » o r^ o^ o> O O> pM( O ^ H* 5, o 01 o> a. 51 CTl H CO H X M 00 w H CO M 5 ?C/3 O M H H JS f* J3 « uJ- 1 ^ • T3 ^ t H r. n « *" c3 G c" »rt S •*-» i 2 3J c £ ^ rt J5 c 'C w rt G .2 rt V i 3 S c rt -| jgffi ^ ^ £ ^»* c H 6 1 1 j IB3 (4 OJ U) rt g Oi C/3 D £• H f3 id (U .^^* *-< s-g frj* rt "—' Iff III 1 H T3 C OS fr 3 &T S i Us b H > TJ •J -' 4J O ^ t! co 9P 315 ii "° tS CG 1 | 1 i , 3 - V 1 i i ™ 1 S^ S e - *§ oT 1 -~ ( 3 c o 1 1 ;° 3" | &| g | S v !•§/§ •Jj 1^1 1 2 Q C < p sis 1 1 OH ^» •e 'd ^ T3 c G T^ c c §^~* C c . a a 8 Himly r Schweizer S_ Is •§*.„!&.« S 2 -5 g,1?^^? 2-i s o^y fl o « ||QQ r Pelouze 8 Schimmel a Co. G 'i (N 2 Atkinson a Yoshida « W •SJ! CJ -M U 5 Bouchardat 8 Kane 4. Schweizer 3 Volckel l|lf| I1 11 4 Baeyer 6 Kay and Per! .6 Perkin n menthone. amphor from c T ro Tt- > CO CO t>- ^ in N -b ii'OO •^- oo oo oo oo c co co crJ" 00 oo £ 00 CO G oo oo oo oo oo o^ o^ 00 00 x o\ o\ o y < H H H H M M I— 1 H H H M H H t M H H H l-l M H H W (J5 T3 ^ ^ G &t "^ ^ CX *>. jcs rt S3 J^ .t! ^QQ u- « U C S i^l'5^ g^S^ffi S § "* ** H 00 00 00 000 | ^ VH flJ r fei se, 8 g 8 881 .5 = £ 5 s ^ o 2- o oo Gluc in, C in, Cjj lin C =: a?o2 i i i ;- a •§ g | I S 4 I CHEMISTRY OF PLANT AND ANIMAL LIFE 147 more whose supposed structure has not been confirmed by synthesis. The first indications of the important natural role of sub- stances containing this group came as early as 1820, when Braconnot obtained a substance " glycocoll " by boiling glue with dilute acids. In the ensuing thirty or forty years various other compounds, which bore more or less chemical resem- blance to glycocoll, were prepared from meat extract, milk, bile and similar animal juices. Liebig, Wohler, Liebreich and others subsequently found that the cause of the similarity lay in the fact that the creatine, tyrosine, asparagine, serine (to name only a few of the compounds in question) were all deriv- atives of the amido-acids. This naturally led to synthetical work on the amido-acids, commenced by Strecker about 1860, and continued by numerous chemists down to Erlenmeyer, Curtius, and especially Emil Fischer, the present-day workers in this branch. In this way it was soon found (cf. the table which follows) that a number of these animal decomposition-products were either amido-acids (e.g. glycocoll, tyrosine), cyclic anhydrides of amido-acids (creatine, betaine), amides of amido-acids (as- paragine, urea, guanidine), or more complicated amido-acid derivatives, such as cystine, tryptophane, or proline (some of the most recently added members). Moreover, the ptomaines or " corpse alkaloids," poisonous products of animal decay, were also found to be closely related to the above (Selmi, 1872), being simple aliphatic diamines. More important than all this, however, are the efforts which have been made with no small success to trace a connexion between such chemically simple end products of decomposition and the complicated components of living bodies known as albu- mens. Various workers have shown within the last twenty years that the molecular magnitude of such substances (e.g. casein, haemoglobin, etc.) is very large, and cannot fall short of 16,000 in most cases ; but.no precise conception of albuminoid struc- 148 A SHORT HISTORY OF CHEMISTRY ture was arrived at until Fischer turned his attention to the problem about 1900, having solved those of the sugars and of the purines (to which we shall shortly refer). His work is too extensive to recount in detail, but it may be summed up in the diagram which he has succeeded in drawing up to show the successive decompositions of an albuminous sub- stance : — ALBUMEN (nucleo-protein) (pepsin | hydrolysis). ALBUMOSE (nuclein) PROTEIN decomposition-products, (trypsin | hydrolysis). PEPTONE (nucleic acid) PROTEIN decomposition-products, (acid | hydrolysis). I Amido-acids, phosphoric acid, purine bases, sugars. From these protein or polypeptide decomposition-products Fischer has isolated definite compounds of the general structure NH2[CH2.CO.NH]n.CH2.COOH, and, on the other hand, he has synthesized chemically similar substances (although of less molecular weight) from simple amido-acids by a variety of methods, obtaining in the latest instance an octadeca- peptide containing fifteen glycocoll and three leucine groups (1907). He has thus shown the general nature of the proteins and, consequently, of the albumens. For a number of years previous to the protein work he was engaged in consummating by decomposition, as well as by synthesis, the knowledge of another group of natural products such as caffeine, uric acid, xanthine, guanine (previously studied by Liebig, Strecker, Baeyer, and many others), all of which he CHEMISTRY OF PLANT AND ANIMAL LIFE 149 proved to be derivatives of a parent substance " purine," © N =®CH 3) N - 0C // CH (8 which he finally prepared (1898). This remarkable work (sugars — purines — proteins) is one of the most complete series of investigations on record in chemical history. Since 1900 W. Traube has also contributed a number of independent syntheses of most of the purines. In the following table the various natural amido-acid or amido-acyl products are grouped according to the order in which they have been discussed above : — 150 A SHORT HISTORY OF CHEMISTRY ^ irffc'.! I Illll O «•> m "i oo oo *& "*£ .H ^^»O ,, ^ efl ^ p1 u Sj i fWl s as-- 1 1 5 lilll II f rj. p^ ^ O .K 3 55 hJ PQQ CHEMISTRY OF PLANT AND ANIMAL LIFE 151 c J CT3 •s II 1 I &z N M O Q\ r^. o o o CO CT> 00 CO 868 Wurtz. 869 Liebreich. && w S si 3 3 r^.j — 1-8 Hi .1 ^ PO »O •J3 5 CTi N »^ VO t^ r-: £ t^oo co oo PM CQ H H H H v . C rt oo H ~*> offee) 1881 Fischer |" {'1865 Strecker {; ski (cocoa) 1 I (1881 Fischer ano) 1861 Strecker ] ncreas) 1897 Fischer -v—v 1 ! CO H -^ 1 'O 2 15 S^^O u ^— ^ *^ 3 Cj i JM IS ( \N] Guanidine, NH = Creatine,NH = (e) Betdines Choline, CH2(OI \/ ffi 0 _c an empirical manner) to manufactures (e.g. Chinese pottery and Egyptian colouring). During the Middle Ages, Italy and France were the most prominent countries in this respect, and later came the modern supremacy of England. Most recently there has been witnessed a remarkable development of industrial operations in Germany, which has given rise to much pessimistic talk in England. But if British manufacturers show more readiness to adopt the latest technical devices, and give adequate support to the facilities now available for the instruction of their THE APPLICATION OF CHEMISTRY 155 workers, little fear need be entertained as to whether our coun- try can " hold its place ". Finally, the modern system of transit, etc., has modified the location of factories, so that whilst in some cases raw material is brought to the centres of civilization for fabrication, in many others the ore, crop, or whatever it may be, is worked up in distant parts of the world close to its natural source. Turning to the purely scientific side of the subject, it will be well to point out how, especially of recent years, purely theo- retical researches have assisted the manufacturer. We may do this best by giving a few concrete examples : — (1) Le Chatelier's work on the " phases " and the thermal conditions prevailing in the blast furnace. (2) The same physical chemist's research on the conditions of equilibrium of the reactions CaCO3^±CaO + CO2 and CO2 ^CO + O. (3) The elaborate electrochemical and thermochemical theories upon which the processes for the " fixation of atmospheric nitrogen " (§ 3) are based. (4) The difficulties (only overcome by years of research) in the practical application of the sulphuric acid " contact process ". (5) Syntheses of various organic compounds have provided means for supplying many products more cheaply (alizarin, indigo, etc.). We will now proceed to give a more detailed account of this practical application of results obtained in the laboratory. § i . The Preparation of Useful Elements. Metallurgy — Taking first the larger branch — metallurgy — of this division, we may divide modern practical methods as follows : — (a) Those which are simply improvements of older fundamental principles. (p) Those which involve entirely new processes (in most in- stances the application of electricity], (a) The principle of the smelting of a few ores, such as those of lead, tin, copper, and mercury, remains the same to-day as 156 A SHORT HISTORY OF CHEMISTRY when directions for making these metals were recorded by Greek and Roman philosophers. These directions were naturally simply of the nature of recipes, the explanation of the different processes being but imperfectly understood all through the al- chemical and phlogistic periods. The alchemists, however, knew sufficient to enable them to use a rough sort of analysis as a check on the purity of their products, the first advice on the subject of assaying appearing in the works of Agricola and Libavius. Modern modifications have consisted here in the use of a " wet process " (Hunt and Douglas) and an electrolytic pre- cipitation process (Elsmore, Siemens, and others) for copper, methods of desilverizing lead (Pattinson, Parkes), and economic improvements in the metallurgy of some other elements, such as zinc (Marggraf, Stromeyer). Among elements which are still obtained by processes cen- turies old we may mention mercury, sulphur, bismuth, and tin- The metals of the platinum group were first isolated on a commercial scale by Cock (1800-1808) in the form of impure platinum ; Deville and Debray constructed a furnace for the fusion of these metals and Matthey showed how to separate and purify them. Before dealing with the iron industry (the most important of this section), we will recall the introduction of electro-plating by De la Rive in 1836 and Jacobi in 1839, a method which was extended during the next generation to the cases of copper, silver, gold, nickel, and manganese, amongst others. The manufacture of iron and steel went on by the old Catalan and allied processes until in 1784 Cort introduced the puddling process for wrought iron ; another important improvement was the substitution of hot for cold air in the blast for the furnaces (Neilson, 1828). Between 1856 and 1867 the Bessemer process for converting cast iron to steel was perfected ; contempor- aneously another method was introduced by Siemens and Martin. These were improved upon by the Thomas-Gilchrist THE APPLICATION OF CHEMISTRY 157 process (1878-80) ; Wagner has shown how the slag from this process, rich in phosphates, may be utilized agriculturally as a manure. Such is a bare outline of one of the most important British industries ; other points of scientific interest include the researches of Bunsen and Playfair on the composition of furnace-gases, and the utilization of the spectroscope by Bradge and Roscoe to detect the end point of the reaction in the Bes- semer process. (b) The newer methods of element manufacture apply as a rule to elements difficult to isolate from their compounds and consist mainly of electrolytic processes and processes involving extremely high temperatures. The first type includes the modern manufacture of the alkali and alkaline earth metals, magnesium, aluminium, etc. Of these, the alkalies were formerly made by violent reduction processes; calcium, strontium,and barium had only been obtained impure by the action of sodium amalgam on their salts, and the rest were made by fusing their chlorides with sodium (Wohler, Deville). The case of the alkali elements is particularly in- teresting ; Davy's electrolytic isolation of these was regarded as of purely theoretical interest, and Gay-Lussac and The"nard tried to manufacture sodium commercially by heating iron with fused caustic soda. Later, in 1823, Brunner showed how potassium resulted from the ignition of an intimate mixture of the carbonate and charcoal; Deville improved upon this by igniting a paste made of soda and chalk with oil. , Such methods were comparatively costly, but the electrolysis of the fused chloride or hydrate on a commercial scale by Castner (1890) furnished a cheap means of preparing the pure elements. A further modification is the electrolysis of the aqueous alkalies with a mercury cathode, with which the liberated element at once amalgamates. The alkaline earth and other elements are all prepared at the present day by electrolysis of their fused chlorides (in the case of aluminium, electrolysis of a solution of bauxite AIO(OH) in fused cryolite A1F3, 3NaF). 158 A SHORT HISTORY OF CHEMISTRY Reduction of refractory oxides at high temperatures has been carried out of recent years by Moissan (a mixture of charcoal and oxide of uranium, tungsten, manganese, chromium, silicon, or titanium being heated in the electric furnace, 1893-6), by Readman and Parker (phosphorus from phosphates, sand, and coke in an electric furnace, 1902), and by the "thermite" process of Goldschmidt (1898), an intimate mixture of aluminium powder and an oxide of iron, nickel chromium, manganese, etc., which on ignition by a thermo-detonator yields the metal and alumina with evolution of much heat. The manner in which of late years manufactories for the pro- duction of the rarer elements and compounds have sprung up is noteworthy ; we may instance those for the rare earth oxides and elements (for Welsbach " mantles," etc.), as well as the new factory in London for uranium and radium compounds. The use of potassium cyanide in gold and silver extraction is a metallurgical improvement which has now been applied for many years. The technical history of a few gaseous elements is also in- teresting ; chlorine, for example, was manufactured on modern lines by Weldon (1868) from pyrolusite, an important addition being the Weldon- Pechiney method of recovering the man- ganese (1882); another method (decomposition of HC1 by heated copper salts) was devised by Deacon (about 1880), while at the present time a large amount of chlorine is produced in the Kellner-Castner electrolytic process for caustic soda from brine (see § 2). Finally, nitrogen and oxygen are now exclusively prepared by the fractional distillation of liquid air, the older methods of depriving air of oxygen by barium oxide (Brin, 1881) and re- covering the oxygen from the barium peroxide formed, having failed to compete successfully with the newer process. § 2. The Alkali, Sulphuric Acid, Vinegar and similar Industries — We have next to deal with a number of industries which usually go by the name of "chemical manufactures," and THE APPLICATION OF CHEMISTRY 159 we may take the " soda industry " as one of the most important instances. Sodium and potassium carbonates were made in olden days by incinerating sea-shore plants ("barilla"), but towards the close of the phlogistic period search was made for a better method. The clue to this improvement was supplied by Guyton de Morveau in 1782, who showed that soda is formed when Glauber's salt is heated strongly with coal and iron. Leblanc (1787-91) based his process upon this observation, preparing the sulphate from common salt and then heating it with coal and chalk, finally obtaining the carbonate from this by washing with water. The system was first worked in England by Muspratt in 1824. Some fourteen years later Dyar and Hemming took out a patent for obtaining soda crystals from common salt by the action of carbonic acid in the form of ammonium carbonate. This was improved by Solvay in 1861 and adopted in 1874 in England at Brunner, Mond & Co.'s works. Finally, Har- greaves and Bird (1896) have introduced an electrolytic method for soda production from salt, using a special electrode per- meable to sodium ions, but not to brine, and supplying a stream of carbon dioxide externally to the electrodes whereby the product obtained is soda crystals or simply caustic soda as required. These two last methods have cheapened soda-fabrication to such an extent that the Leblanc process is now only valuable for its bye-products — hydrochloric acid, first collected as an aqueous solution from the conversion of the salt to sulphate by Gossage (1836), and sulphur and sulphides of calcium, utilized by the recovery processes of Chance (1888) and others. Caustic soda itself used to be made technically (from 1850 onwards) by " causticising " soda solutions with lime, filtering from chalk and concentrating. About 1885 the Castner-Kellner process of electrolysing brine with a movable mercury cathode came into operation ; the mercury is first made to act as cathode and then decomposed by water by mechanical oscillation. Later 160 A SHORT HISTORY OF CHEMISTRY processes have all been modifications of the electrolytic prin- ciple. We have just indicated the chief source of hydrochloric acid ; of the other two most important mineral acids there is little of note in the preparation of nitric acid (for which Boyle gave the first technical directions) except the recent electrical methods mentioned in the next paragraph. The means of producing oil of vitriol, on the other hand, have varied a good deal. First manufactured by the Nordhausen method (distillation of green vitriol) in alchemical times, a great improvement was effected in its fabrication by Roebuck (1746) at Birmingham, Gay-Lussac (1824), and Glover (1841), who evolved between them the " lead chamber process ". More recently this has been in part superseded by the " contact process," in which sulphur dioxide and oxygen unite by the catalytic action of finely-divided platinum. A patent covering this method appears under the name of Philips as far back as 1831, but it was not till about 1875 tnat a practical paying process was devised (Winkler, Knietsch). Since 1900 the Badische Anilin und Soda Fabrik have improved it in various directions, such as eliminat- ing traces of arsenic (which " poisons " the platinum) from the mixed gases, and employing sulphates of cerium, lanthanum, and other rare earth metals as additional catalysts. Of other inorganic chemicals produced in large quantities " chloride of lime " (bleaching powder) may be mentioned. The commercial process was designed by Thenard in 1799 and carried out by Tennant & Co. in England. About the same time Berthollet introduced his "Eau de Javelle " (aqueous sodium hypochlorite). It may be remarked that the constitu- tion of bleaching powder was quite unknown till about 1835, when Balard suggested the formula CaCl(OCl). Turning to the more common organic products, we find that alcohol ("spirits of wine," "aqua vitae ") has been obtained from wines from the earliest times by simple redistillation, though in this way it never attained a strength of more than THE APPLICATION OF CHEMISTRY 161 92 per cent. During the past century, and more particularly since about 1875, when the phylloxera began to increase its ravages amongst vines, beet-sugar and potatoes have been the source of most of the alcohol supply. Still-heads for im- proving the fractionation process are due to Argand, Adam, and Blumenthal ; Gay-Lussac systematized alcohol analysis (" alcoholometry ") in 1824. The essences or ethereal oils (in many cases ethyl esters) have always formed a branch of chemical industry, but as the improvements deal chiefly with mechanical appliances for ex- pressing or distilling the different plant-juices, we will merely remark here that Vaudin introduced vacuum distillation into essence works in 1879, and that since 1885 Schimmel & Co. have been the pioneers in this branch of the technical science. Vinegar used to be made from alcohol by Boerhave's fer- mentation method (1720), known as the " slow " or " Orleans process"; in 1823 Schiitzenbach and Wagemann introduced the German or quick vinegar process. Acetic acid itself was first made on a large scale by distillation of wood by the patents of Kestner and of Halliday (1848), the purification of the pyroligneous acid by lime being due to Mallerot. Cane-sugar came originally from Asia and was introduced to Southern Europe and Africa by the Moors ; thence it was trans- ferred to the Central American islands by the Spanish and Portuguese colonists, and at the present day it is a decaying industry in those regions, owing to the introduction of beet- sugar. The presence of sugar in beet-juice was discovered by Marggraf in 1747, but the first technical means of extracting it were found by Achard in 1779. The first factory was started in France in 1796, and until about 1836 the bulk of the beet-sugar came from French soil ; since then, however, Austria-Hungary, and especially Germany, have taken the lead. Filtration of the raw juice through mineral charcoal was intro- duced by Figuier (1811), evaporation of the syrup under ii 1 64 A SHORT HISTORY OF CHEMISTRY countries since the seventeenth century. Of improvements in its fabrication, we may note the introduction of plate glass by de Nehan in 1688 (an improved process was devised by Pelou/e in 1856), the substitution of sand projected under great pres- sure for hydrofluoric acid in engraving by Tilghman in 1870, and the advances effected by Siemens in the fusion process. Modern glass usually contains much more soda and corre- spondingly less lime than the older varieties. In 1869 Em- merling and Bunsen contributed some important work on the solvent action of water, acids, alkalies, and various salts on specific kinds of glass. The phenomenon of devitrification was first observed by Reaumur, about 1770. Earthenware, again, was certainly used by the Chinese as well as by the Egyptians, but pottery impermeable to water has only been known since the eleventh century of our epoch, while the finer kinds of earthenware first appeared some 300 years later (the Moors in Spain, and the Italians, notably L. della Robia, 1411-1430) ; Palissy's great improvements in this branch took place about 1550. Porcelain was introduced from China about 1 600, and a century later Morin made efforts to reproduce the Chinese excellence at Saint-Cloud ; Wedgwood was at the zenith of his fame as a potter about 1750, and a decade or so later the famous Sevres porcelain was first manufactured, owing to the efforts of Reaumur, Macquer, and others. In 1800 Spode commenced the custom, which has remained practically con- fined to English potteries, of substituting bone ash for a part of the kaolin or clay otherwise used. Of recent years Seger (1892) has still further improved the manufacture of earthen- ware, and much research has been carried on with the aim of elucidating the chemical structure of clays. There is not a great deal of interest attaching to the history of cements ; four general classes are recognized at the present time : lime, Roman cement, Portland cement (which is an artificial mixture approximating in composition to the older Roman kind) and hydraulic icements. The latter require the THE APPLICATION OF CHEMISTRY 165 addition of water to make them "set" ; they were introduced about 1 800 in England and contain lime with an abundance of alumina. Improvements in hydraulic mortars were made, notably by Winkler and Knapp, a few years ago ; theories of the manner in which cements " set " by atmospheric action have been discussed during the past quarter of a century by Le Chatelier, Newberry, Rebuffot, and others. § 5. Paper, Matches, Heat, and Light— The use of cotton fabrics for paper manufacture did not commence to supersede the old papyrus and parchment in Europe till the eleventh century, although in China it was used long previously. The oldest mark on cotton paper is dated A.D. 1050. Paper manufacture became general in France and Bavaria about 1400, but all paper in England was imported until 1588. In 1750 Baskerville produced "vellum paper". Later improve- ments may be summarized as follows : the introduction of machinery (1803), improved by Dickinson (1809); production from different trees (palms, bananas, etc.) (1839-1851); pro- duction from wood-pulp or straw (1846), rendered practicable by the processes of Wolter (1867), Aussedot, and Tessie. Paper used to be bleached by chlorine gas, but of late years a better and safer electrolytic method has been adopted. The first matches, other than the primitive flint and tinder, were made of .a mixture of potassium chlorate and sulphur ("chemical tinder," 1807), which was dipped in oil of vitriol to effect ignition. Their use was not, it is believed, very extended ! In 1833 Romerand Moldenhauer introduced phos- phorus matches, while the original form of the modern safety- match, in which red phosphorus is used (and usually only on the prepared surface of the box), dates from 1848. Of late years legislation has in some degree helped to eliminate the older forms of poisonous matches, containing yellow phosphorus. A very important modern industry is that of india-rubber (first introduced into Europe in 1736), the raw material ema- nating chiefly from Para, Peru, Central America, and the 1 66 A SHORT HISTORY OF CHEMISTRY Congo. The most interesting development, chemically speak- ing, is the process of vulcanization by means of sulphur, dis- covered by Goodyear in 1839. Many attempts have been made to effect its synthesis, and Harries appears recently to have succeeded. The ancient source of heat for domestic purposes was wood, and although coal was known to the Greeks and Romans it was not greatly used as a combustible until towards the middle of the eighteenth century, when the introduction of machinery into the arts created a demand for a cheap fuel. Coke was first manufactured in 1769. It is almost needless to point to the uses made of coal-gas and electricity for heating purposes during the last fifty years, but we may enumerate a few gas fuels used for technical purposes at the present day, such as "producer gas" (CO and N2, by partial burning of coal in insufficient air), " water-gas " (CO and H2, by blowing steam over red-hot coke; a very hot flame, useful technically), " mixed gas " (CO, H2 and N2, by blowing air and steam over burning coal; cheap and hence useful in small works), and " Dowson gas," which is practically synonymous with the last. The problem of illumination has several times had a curiously beneficial effect by indirectly throwing light upon purely theo- retical questions. A commission to improve the means of lighting the Paris streets turned Lavoisier's attention to the sub- ject of combustion, and again, Dumas' efforts to elucidate the nature of annoying fumes emitted by chlorine-bleached candles at a French state function led to his discovery of substitution in organic compounds. Of general inquiries into the nature of luminosity, Sir H. Davy's (inventor of the miner's safety-lamp) and Frankland's have been most useful. With regard to specific illuminants, candles made from tallow (stearic or palmitic acids from fat by lime or, later, sulphuric acid) and subsequently wax (solid paraffins and plant waxes) come first in chronological order. Oils of varying kinds were also used — at first aromatic, scented oils, and in more modern times, petroleum from THE APPLICATION OF CHEMISTRY 167 Russian or American wells. At present the distillation of petroleum ranks second in importance to that of coal, and yields (in descending order of volatility) gasolines for motor- engines, petroleum ether, naptha or ligroin for lighting and solvent purposes, machine-oils, and finally, " heavy oils," semi- solid greasy materials useful as lubricants. Caucasian petroleum is made up mainly of hydroaromatic hydrocarbons, American of aliphatic or paraffin hydrocarbons. Finally we come to coal-gas, introduced in 1792 by Murdoch, first made on a large scale six years later, and used in lighting London streets by Winsor in 1813. Experiments were made intermittently and unsuccessfully from 1800 to 1850 to use cheaper forms of gas, such as oil-, peat-, or water-gas. Tech- nical improvements in coal distillation continued to be made until about 1880, but since that date no fundamental change has been made in the method as perfected by Lunge, which, in its most efficient form, permits of the utilization of " raw gases " (for heating), coal-gas, gas-liquor (source of ammonium salts and sulphides), tar (to be re-distilled) and coke residue. The distillation of the coal-tar (first carried out by Clayton in 1738 and later, in France, by Lebrun in 1786) has grown to be a most important industry ; the tar itself is used for protect- ing iron, wood, ships, etc., against air and water, as an artificial asphalte (mixed with sand), and in various other ways, while its distillation products include benzene and many other aro- matic hydrocarbons of boiling-points ranging from 80° to 300° C, and technically important substances (especially to the dye in- dustries) such as phenol, naphthalene, anthracene, pyridine, carbazole, and a host of others. The introduction of rare earth oxides in the form of " in- candescent " mantles is due to Welsbach (1885) ; improvements both in the composition of the film of oxide and in its mechani- cal arrangement continue to appear. § 6. Dyes — Indigo, madderwood and a few mineral colours such as minium, cinnabar, rouge, orpiment, realgar and 1 68 A SHORT HISTORY OF CHEMISTRY galena were known to the ancients, judging from their writings (e.g. Pliny). There is not much to record during the alchemistic period, though isolated workers, such as Glauber, occasionally investigated dyeing processes. The use of mordants (alum, iron salts) became known during this epoch, but their precise mode of action is even now imperfectly understood. Macquer was the first chemist to look into this problem (1795). A table showing the chief mineral and other dyes manufactured at the opening of the modern era may be useful : — Chetnical Nature. Artificial Preparation. Cobalt blue (smalt) 1650 Schiirer (fusion of glass and cobalt residues) Prussian blue Fe4[Fe(CN)6]3 1704 Diesbach Alizarin 1750 From madder plant in Europe Zinc white ZnS 1790 Courtois White lead Pb(CO3)3 (basic) 1801 Th^nard Schweinfurt green Cu(C2H3O2)3, 3Cu(AsO2)2 1814 Sattler Ultramarine From sodium silicates and 1828 Guimet; Gmelin (for- sulphur merly from lapis-lazuli) The more recent history of organic dyestuffs is bound up, as is well known, with the exploitation of the coal-tar products. Faraday, Laurent, and Runge (1834) are prominent among those who isolated valuable hydrocarbons from tar, while Hof- mann (1843-5) discovered aniline and its homologues therein. In 1856 Perkin obtained mauve (magenta) by the oxidation of aniline with chromic acid, and since then innumerable synthetic dyes have been produced, not only from coal-tar products (though these form the basis of the most widely-applied colours) but from other common aromatic substances as well. We should note especially the device, very soon introduced, of improving the solubility of a dye by increasing its acidity (sulphonation) or basicity (alkylation). The evolution of the various colouring matters can best be grasped by a chrono- logical table: — THE APPLICATION OF CHEMISTRY 169 3 § -2 3 \_x ^^•=^X < i 1! il Hi ijs < «|| c !|£ •8l<5o J-sJj Ig | g 1 If^ll0" llfft If itlll 11 liilllfl s< • I "rt 6 ^ Amidophe 0rt g g j U HH i yo A SHORT HISTORY OF CHEMISTRY If we now add another summary, showing the theoretical development of the formulae of the various parent compounds concerned, it will be unnecessary to emphasize further the dependence of modern industry on the research laboratory : — Class of Substance. Chief Investigations. Aniline and homologues 1834 Mitscherlich (C6H5NO2) ; 1834 Runge ; 1841 Zini 1852 Bechamp(C6H3NH2) ; 1845 Hofmann and Mu pratt ( p-Toluidine) Azo-bodies Griess, 1859 (diazo reaction) ; 1862 (diazoamidobenzem 1866 (amidoazobenzene) Indigo Constitution by Baeyer and his students, 1865-1874 Alizarin Constitution and subsequent synthesis by Graebe ai Liebermann, 1868 Acridine Constitution and synthesis by Graebe and H. Caro, 18' Triphenylmethane Constitution and synthesis by Kekule and Franch mont, 1872 Phenazine Constitution and synthesis by Claus, 1873 Phenthiazine (thiodiphenyl- Constitution and synthesis by Bernthsen, 1888 amine) Phenoxazine Constitution and synthesis by Bernthsen, 1887 Flavones and Xanthones Constitution and synthesis by St. v. Kostanecki, A. ( Perkin, 1895-1905 § 7. Explosives — Van Helmont, whose explanations of chemical processes have several times attracted attention by their clearness, ascribed the characteristic effect of exploding gunpowder to the production of much gas ; study of the evolved gases in this and other explosive reactions was not greatly en- gaged in, however, until the nineteenth century, during which their composition under varying conditions was made the sub- ject of research by Debus, Bunsen, Abel, Nobel, and others. Berthelot's work on the thermo-chemistry of explosives is very important. Of the individual members of this class gunpowder has of course been longest known, having been employed in fireworks by the Chinese and Moors. After its rediscovery by Schwarz in 1334 it came to be employed in warfare by the occidental THE APPLICATION OF CHEMISTRY 171 nations. It has remained practically the only explosive in which the oxygen necessary for combustion is supplied by means of an added substance (the nitre), unless we include a disastrous attempt of Berthollet's (1786) to substitute chlorate for nitre. The more modern type, which consists usually of a carbon compound containing sufficient easily available oxygen for complete combustion, includes the fulminates, discovered by Howard (1800), characterized by Liebig and introduced as de- tonators by Ure (1831) ; the picrates, investigated by Fontaine, Designolles, and Abel ; nitrocellulose (gun-cotton), discovered by Braconnot in 1823, and prepared by Schonbein in 1846 (Pelouze (1838) suggested its use in artillery, but much difficulty was found in manipulating it until in 1886 Vieille discovered the secret of detonating it safely) ; and nitroglycerine, first produced by Sobrero in 1847. The latter was first applied as dynamite (after absorption in kieselguhr) in 1862 by Nobel, Abel, Champion, and others, while mixed with gun-cotton it has been applied by these chemists and others, such as Vieille (1884), to the fabrication of smokeless powders (e.g. Nobel's mixture (1890) of gun-cotton, dynamite, and gelatine). CHAPTER X THE HISTORY OF PHYSICAL CHEMISTRY WE have to deal in this chapter with the direct application of physics to chemistry, and within the last thirty years so much progress has been made in this region that the bulk of the work which we shall chronicle will have been carried out during that period. At the outset we should note that the basis of the whole science rests on two " laws " — the conservation of mass and the conservation of energy. The first of these was proved by Lavoisier when he showed that in chemical reactions matter is never either created or destroyed, but quite recently (1893-1908) elaborate experiments have been carried out by H. Landolt in order to test how far the law is an accurate expression of fact, the final result being that it is rigidly correct to within the limits of one part in ten million. The accompanying doctrine of the conservation of energy is due more to Mayer and to Joule (1842) than to any other physicists, though not a few workers dealt with the subject in the earlier part of the nineteenth century. § i. The Physical Chemistry of Gases— The first to realize the varying chemical nature of different gases were van Helmont (who introduced the term "gas" about 1620) and Rey (who showed that air possessed weight in 1630). The relation of the volume of gases to external pressure was dis- covered by Boyle (1660) and Mariotte (1670), while the effect 172 THE HISTORY OF PHYSICAL CHEMISTRY 173 of temperature was quantitatively investigated by Charles (1785) and Gay-Lussac (1808). Dalton (1807) showed that, in any mixture of gases, each exercised its own "partial pressure" independently of the rest. Again, in 1808, Gay-Lussac found that the volumes of reacting gases always bore a simple ratio to each other and to the volume of the products (if gaseous), and this served in certain cases to contradict Dalton's atomic hypo- thesis (cf. p. 33) until in 1811 Avogadro put forward the hypothesis that equal volumes of gases contained equal num- bers of molecules (Ampere attempted to extend the same hypothesis to solids, with indifferent success, a few years later). In the meantime, from a purely physical standpoint, others were developing the kinetic theory of gases. The idea that gas particles are in motion was expressed by Bernoulli (1738) and Herapath, but a physical estimation of their mean velocities was first made by Joule in 1851. The modern kinetic theory of gases was practically stated by Waterson (1845) in an un- published paper which was only brought to light in 1892 by Lord Rayleigh, and consequently the fame of evolving the theory rests with Clausius (1857) and Maxwell (1860). From this in 1 88 1 van der Waals constructed a modified form of the " gas -equation " PV = RT (Horstmann), which should express the deviations from Boyle's and Gay-Lussac's laws shown by readily liquefiable gases, and also to a smaller extent (Amagat, 1880) by the then-called permanent gases (nitrogen, hydro- gen, oxygen). This equation, \P + ~i)(v ~ b) = RT (where a and b are specific constants), is so accurate an expression of fact that by its means, on the one hand, Guye and Friedrich were able in 1900 to deduce practically coincident values for the " gas-constant " R from measurements of different gases, and, on the other, Daniel Ber- thelot (1899) has theoretically calculated the atomic weights of 174 A SHORT HISTORY OF CHEMISTRY various elements from the densities of their compounds (or of the elements themselves) determined by Regnault (1845), Lord Rayleigh (1888), and others. The values so obtained agreed excellently with those from chemical data. The liquefaction of gases was a subject of careful study by Northmore (1805), who liquefied chlorine, and by Michael Fara- day (1823), who condensed ammonia, sulphur dioxide, and other gases by the combined application of considerable pressure and a freezing mixture. His principle was improved by later workers, such as R. Pictet (1877), Cailletet (1877), Wroblewski and Olzscewski (1883), and, finally, Dewar (1884), by increasing the pressure and the degree of cold, so that all the known gases (even the so-called permanent ones), with the exception of hydrogen and helium (discovered later), had been liquefied by 1885. Dewar succeeded in liquefying hydrogen in 1898, and in the meantime a new principle (Hampson-Linde, 1895, the intense cooling of a gas by its own expansion when already cooled under great pressure) led to the cheapening of liquefac- tion processes. Finally, H. Kammerlingh Onnes condensed helium in 1908 to a colourless liquid boiling at 4'5° Abs., and has also obtained it in the solid state. In 1821 Cagniard de la Tour noticed that many gases could not be liquefied above a certain temperature by any pressure, and in 1869 Andrews minutely studied the phenomenon and found that for each gas there existed a temperature above which no amount of pressure would condense it ; he called this the critical temperature and the pressure necessary to produce lique- faction at that temperature the critical pressure, while the specific volume of the liquid formed was the critical volume. Much important theoretical work has since been carried out on the critical data, notably by Mendelejew (1884) and by Ramsay and Young (1894). Finally the decomposition of some gases by heat and their reformation on cooling was studied by Deville in 1857 and named "dissociation ". About the same time Kopp and Kekule THE HISTORY OF PHYSICAL CHEMISTRY 175 observed the effect and set it down to partial decomposition. Gaseous dissociation has been studied quantitatively by methods of effusion (sal ammoniac, Pebal, 1862), colorimetry (phosphorus pentachloride, Deville ; nitric peroxide, Salet, 1868), and specific heat (nitrogen peroxide, acetic acid vapour, Berthelot and Ogier, 1882). § 2. Crystallography — This sub-science, so important for mineralogy, was given a definite shape by Rome de L'Isle, Hauy, and Werner, who in the early years of the nineteenth century classified crystals according to physical form and assumed that difference in form entailed difference in chemical composition. This was overthrown later by Mitscherlich's discovery of poly- morphism (1821). Later crystal-systems, by means of which all crystal-forms were finally divided into thirty-two geometrical classes, are due to Hessel (1830), Gadolin (1867) and P. Curie (1884). In 1888 Reinitzer noticed that cholesteryl benzoate, before melting to a clear liquid, passed through a turbid or milky phase, and in 1890 other instances were observed by Gattermann. Lehmann (1890) found that the turbid liquid rotates the plane of polarized light, and must therefore be doubly-refracting and possess crystalline structure. Such substances are said to be liquid crystals, and although Tammann (1901) disputed the crystalline structure, the previous explanation is usually adopted at the present time. The relation of crystalline form to chemical composition has naturally been the subject of much study. In 1846 Buys-Ballot stated that the elements and simpler compounds tended to crystallize in the simplest forms (regular and hexagonal) and more recently Retgers has statistically demonstrated the truth of the proposition (1892). Before this, however, Mitscherlich discovered isomorphism (1819), following on Gay-Lussac's and Bendant's observations on the growth of potash alum in am- monia alum, and of ferrous sulphate in copper sulphate solutions respectively. Mitscherlich based his views of isomorphism on 176 A SHORT HISTORY OF CHEMISTRY phosphoric and arsenic acid salts, selenic and sulphuric acid salts, and the alums and oxides of iron, chromium, and aluminium, and, with Berzelius, held that isomorphous bodies contained similar atomic structures — a point utilized by Berzelius to assist in determining atomic weights. Fuchs, similarly, discussed the constitution of isomorphous minerals (1872). Finally, reference must be made to Mitscherlich's further dis- coveries of dimorphism and polymorphism (1821), and to Scherer's use of the term polymeric isomorphism (when atoms had been replaced by an atomic group to form an isomorph). Kopp's work on the specific volumes of isomorphs is note- worthy. Other interesting points are the phenomenon of isogonism or hemihedry observed by Pasteur in 1861, wherein the slightest change of constitution (change of asymmetric configuration) causes a similar change in the position of the crystal facets, and that of morphotropy, studied by Groth (1876) — the definite alteration of form caused by definite substituents in organic compounds, especially in the aromatic series. In conclusion, we have to describe the comprehensive theory recently elaborated by Barlow and Pope (1906), who "regard the whole of the volume occupied by a crystalline structure as partitioned out into polyhedra, which lie packed together in such a manner as to fill the whole of that volume without in- terstices. The polyhedra ... are termed the spheres of atomic influence of the constituent atoms." The crystalline forms of many of the elements and simpler compounds, at all events, agree with the postulates of this theory, which is also capable of furnishing a steric formula for benzene expressing, according to the authors, all the necessary chemical facts (cf. chap. vi. p. 99). § 3. Solutions — The study of mechanism of solutions has almost always been developed from an electrolytic point of view, and therefore we may pass over the earlier history of this branch by referring to the theories of electrolysis dealt with in chap, iv., THE HISTORY OF PHYSICAL CHEMISTRY 177 § 4. We are thus left with the discussion of the osmotic pressure of solutions, a field opened up by the work of Pfeffer (1877) who made use of Traube's "semi-permeable mem- branes" (1867). Pfeffer found that substances in solutions obeyed definite laws with reference to their osmotic pressure, etc., but it was van 5t Hoff who first perceived that dilute solutions are amenable to the same laws as gases, and that hence, among other corollaries, it follows that the molecular weight of a dissolved substance is related to the vapour pressure of the solution. This led to the determination of molecular weights by lowering the vapour pressure of a solvent (Raoult, 1887) or, what amounts to the same, lowering of freezing- point or elevation of boiling-point ; it then appeared that solutions of electrolytes in water gave abnormal values for the molecular weight, and this found an explanation in Arrhenius' ionic theory (1886), which assumed that ions exist ready formed in dilute solution, the electric current exerting simply a directive effect. This does not, however, afford an absolutely perfect explanation, and it seems likely that the final theory of solutions will be a combination of Mendelejew and Arrhenius' theory of hydration of ions and molecules (1888) for concentrated solu- tions, with the ionic theory for dilute solutions and electrolysis. The electrical conductivity of solutions has been the subject of experiment ever since Hittorf (1853-9) determined the " trans- port numbers " for the migration of the ions and Kohlrausch (1879) discovered, first, the relation of the " transport number " to conductivity (1879) and then the law of the " independent migration of the ions" (1885), whereby the total conductivity of a solution was shown to depend upon the sum of the two ionic velocities. The conductivity of acids (organic, Ostwald, 1878-87 ; Walden, 1891 ; very weak acids, Walker, 1900) has been shown to be a measure of their "relative affinity," as already described (chap. iv. p. 57), while that si pure water has been concordantly determined by the E.M.F. of an acid- alkali cell (Ostwald, 1893), the hydrolysis of salts (Arrhenius, 12 178 A SHORT HISTORY OF CHEMISTRY 1893), and the rate of hydrolysis of methyl acetate in pure water (van 't Hoff and Wiis, 1893), and finally, by direct measurement (Kohlrausch and Heyd wilier, 1894). Amphoteric electrolytes (both acidic and basic, such as methyl orange, sulphanilic acid, glycocoll, zinc hydroxide and other feebly acidic metal oxides) have been studied by Kiister (1892), Winkelblech (1901), J. Walker (1904), and many others ; similar fields have been opened by Hantzsch in the case of psetido-acids ami fasts (iBgfyd p. 104), and Noyes and Whitney on complex ions ("double salts") in 1894. Conductivity in solvents other than water has been investi- gated by Tessorin (1896, formic acid), Carrara (1896, acetone) and especially by Jones (1902-6) and by Walden (1901-6, tetra ethylammonium iodide in liquid sulphur dioxide, sulphur oxy- chloride, ether, etc. etc.), while Kahlenberg (1902-3) has proved that the dissociating power of a solvent depends directly upon the magnitude of its dielectric constant. Finally, Nernst has recently given theoretical explanations of " Volta's pile " and of the ordinary galvanic cells by means of a diffusion theory based upon van 't Hoffs theory of solutions. The solutes we have so far dealt with are all crystalline sub- stances, but we must now refer to another branch of soluble bodies, the colloidal substances. The purification of these has been rendered possible by the process of dialysis, discovered by Graham in his researches on diffusion. The phenomenon of diffusion seems to have been first noticed by Parrot in 1815, and a mathematical treatment of the subject appeared by Ficks in 1855. In the meantime the different rates of diffusion and effusion of gases had been studied by Graham in 1851, and later the same chemist extended his ob- servations to the diffusion of dissolved bodies through animal membranes. He found that these were permeable to one set of substances (crystalloids) and impermeable to others such as dextrin, silicic acid, tannin, which he termed colloids (1862). Work on osmosis by Jolly, Briicke, and Pfeffer (1877) proved THE HISTORY OF PHYSICAL CHEMISTRY 179 that the osmotic pressure of such bodies was very small, and consequently their molecular weight should be enormously large, that of many being greater than 10,000 (Linebarger found by osmotic pressure measurements in 1892 that tungstic acid, one of the simpler colloids, possessed a molecular weight of 1700- 1720; (H2WO4)7 = 1750). Much work has been done of late years on this subject (especially by Bredig, 1903, and Billitzer, 1903), but the structure of colloids remains very uncertain indeed and we will therefore simply recall Sabarejew's division of col- loids (1891) into those of molecular weight greater than 30,000 (starch, silicic acid, iron hydroxide, etc.), and less than 30,000 (dextrin, tannin, molybdic acid, etc.). § 4. Molecular Weight Determination — It may be use- ful to give a summary of the physical methods lately developed for its estimation of molecular weight ; these depend mainly on determination of vapour density or of osmotic pressure (direct or indirect). (a) Vapour Density Methods. — The theory of these methods depends of course mainly upon the application of Avogadro's hypothesis; it must be remembered, however, that, while in former times the approximate determination of vapour density was made to serve as a check on the multiple of the chemically- determined equivalent which was to be accepted as the true atomic or molecular weight (Cannizzaro, 1858), more recently the application of van der Waal's equation (D. Berthelot, 1899) has led to exact determinations of molecular weight by gas density in numerous instances. Four different principles have been utilized in succession for the experimental determination of vapour density : — Measurement of the weight of a given volume of an already gaseous substance (Regnault, 1845; Lord Rayleigh, 1888-; Leduc, 1892-8; Morley, 1895). Measurement of the weight of a given volume of vapour (Dumas, 1827 ; applied by Dumas and by Mitscherlich to the elements sulphur, arsenic, phosphorus and mercury). i8o A SHORT HISTORY OF CHEMISTRY Measurement of the volume of a given weight [Hofmann, 1868, designed an improved form of Gay-Lussac's apparatus (1801), which was further modified for high temperature work by Ramsay and Young (1885)]. Measurement of the volume of air (at atmospheric tempera- ture and pressure) displaced by the vapour from a given weight of substance (Victor Meyer, 1878). This has been found to be most generally applicable, especially for very high temperatures (up to 1900° C., Biltz, 1896; 1700° C, Nilsonand Pettersen, 1889). By this means the atomic weights of silicon, beryllium, thorium and germanium, amongst others, have been established from the vapour densities of their chlorides, while the dissocia- tion of compounds like aluminium1 chloride (A12C1G) and stannous chloride (Sn2Cl4) into simpler molecules has also been studied (V. Meyer, Nilson and Pettersen). (b) Osmotic Pressure Methods. — The discovery of the con- nexion between osmotic pressure and molecular weight was re- corded in the last paragraph, and some account will now be given of the practical application of the principle. Guldberg (1870) and van 't Hoff (1886) independently deduced from the laws of vapour pressure that the depression of freezing-point and elevation of boiling-point were both proportional to altera- tions of vapour pressure, and it appeared later that both depend on the osmotic pressure, and hence, on the molecular weight of the solute. This led to four new methods of molecular weight estimation : — (i) Direct Measurement of Osmotic Pressure of Solutions. — This is chiefly of theoretical interest, since it is difficult to obtain a great degree of accuracy. Pfeffer (1877) used semi- permeable membranes of cupric ferrocyanide, Tammann (1888) utilized drops of potassium ferro-cyanide in copper sulphate solution, and de Vries (1888) taught how to prepare isotonic solu- tions by observation of the behaviour of certain plant-cells therein (plasmolysis), and obtained in this way a good determination of the molecular weight of raffinose (C18H32O16). THE HISTORY OF PHYSICAL CHEMISTRY 181 The Earl of Berkeley and Hartley (1906) have recently made important additions to the knowledge of osmotic pressure, (ii) Indirect Measurement of Osmotic Pressure of Solutions.— 1. Lowering of vapour-pressure of solvent (Raoult, 1887; also difficult to manipulate with sufficient accuracy). 2. Depression of freezing-point of solvent. Blagden (i 788) and Riidorff (1861) noticed that the depression was proportional to the amount of dissolved substance; Coppet (1871) and Raoult (1882) saw that molecular amounts of different solutes depressed the freezing-points of a given solvent to the same extent; Beckmann (1888) devised a convenient form of ap- paratus with a specially delicate thermometer, in both of which sundry alterations have been made by later workers ; and Ver- net and Abegg (1894) further developed the mathematical theory of the process. 3. Elevation of boiling-point of solvent (Beckmann, 1889). The last two methods have found a great sphere of utility. § 5. Relation of Physical Properties to Chemical Con- stitution : (a) Mechanical — Here we have to deal once more with a problem whose general importance has only been realized within the last twenty or thirty years, namely, the dependence of the physical properties upon the constitution of compounds. It is now, however, generally admitted that this is a subject of extreme importance to the development of theoretical chemistry. A definite systematization of such pro- perties was not known until Ostwald in 1891 defined them as additive, depending simply on the atomic composition of the molecule — mass is the only perfect example — constitutive (in- fluenced by the mode of union of the atoms — optical activity and absorption spectra are perhaps the most striking instances) and colligative (depending on the number of molecules — vapour density, osmotic pressure, etc.). We shall now proceed to give a very brief and necessarily incomplete resume of the development of the present views on different types of properties, and will commence with those i8a A SHORT HISTORY OF CHEMISTRY which, for want of a better name, may be called mechanical properties. (a) Specific Gravity ; Specific a?id Molecular Volume. — The methods devised by physicists for measuring the density of gases have already been summarized ; the specific gravity of liquids used to be generally measured by the specific gravity bottle, but more refined methods have been introduced by Sprengel and Ostwald (1873, the pycnometer), and by Kohlrausch and Holhvachs (1894, the areometric method, based on Archimedes' principle). The density of solids is not so easy to obtain with perfect accuracy, but the principles chiefly used have been that due originally to Archimedes, and that whereby the solid is made to swim free in a liquid mixture, whose composition is suitably adjusted by means of a heavy component (e.g. methylene iodide) and a light component (e.g. benzene). This device was brought to a high degree of perfection by Retgers in 1889. The specific volumes of elements and compounds were first systematically studied by Kopp (1842-1855), who claimed that it was a purely additive function. Later work by Schroder (1880), Lossen (1882), Horstmann (i 886-8), and others, not- ably Traube, has shown that although Kopp's view is roughly correct, definite modifications are introduced by constitutional influences. Researches on the specific gravity of liquid mixtures (Linebarger, 1896) have also proved interesting, since in many cases evidences of " association " or loose molecular combination have been found. (If) Surface Tension. — The phenomena of capillarity were ex- plained by Young in 1804, and attention has frequently been paid to the property since, its measurement having been effected by Laplace, Gay-Lussac, J. Traube (1891), van der Waals (1894), and others. The temperature coefficient J has been shown to be constant for nearly related members of the same homologous series and its utility as a means of testing the THE HISTORY OF PHYSICAL CHEMISTRY 183 molecular complexity of liquids has been proved by Eotvos (1886), and by Ramsay and Shields (1893). (c) Internal Friction. — The viscosity of gases has been chiefly studied, from a physico-chemical standpoint, by L. Meyer (1879), and Staedel (1882), while much work has been done with respect to solutions by Ostwald (1891), who designed a convenient viscometer, and to liquids by Thorpe and Rodger (1894-6), and to liquid mixtures of many types by Dunstan (1904 onwards) and his students, and in lesser degree by numerous other workers. The fact that molecular association can take place in solid as well as in liquid mixtures has been shown by Trouton and Dunstan (1908) in the case of certain alloys, the method used being the stretching of a wire of the substance in question by a given weight. (d) Melting-point. — Attempts have from time to time been made to give quantitative rules for melting- and boiling-points, but with very little success. The most notable regularities are that the property is affected very little by pressure (Kelvin, 1850) ; that several series of organic acids are characterized by the melting-points of the odd members of the series lying on one curve, while those of the even members are on another (Baeyer, 1877) ; that in aromatic compounds, nitro-substituents melt higher than bromo-derivatives, and these, again, higher than the corresponding chloro-bodies (Petersen, 1874), and a para-substituted compound melts in general higher than either the meta- or ortho-derivative (Beilstein, 1886). The only accurate methods of melting-point determination are the immersion of a delicate thermometer in a large amount of the heated solid, or of the super-cooled liquid (Landolt, 1888). (e) Boiling-point. — Kopp sought to show that equal differ- ences in constitution produce equal differences in boiling-point (1845), but soon found that this was a very limited rule. Re- gularities have been found also by Tollens (1869), Marckwald (1888), Henry (1888), Earp (1893), and others; the general result being : — 184 A SHORT HISTORY OF CHEMISTRY (i) Increase of molecular weight tends to increase the boiling- point. (ii) In organic isomers, the normal compound has the highest, and the most compactly arranged molecule the lowest boiling-point. (iii) A substituent in a central position in the molecule tends to volatility. In 1891 Vernon suggested that many irregularities were due to polymerization and from the behaviour of different series estimated the degree of polymerization of water, sulphuric acid, sulphur, and other substances from their boiling-points. The relation between boiling-point and critical temperature was made clear by Thorpe and Riicker (1884). § 6. Relation of Physical Properties to Chemical Constitution : (H) Electrical — We have already discussed the most important electrical property (conductivity) in con- nexion with the history of electrolysis (pp. 56ff.), and we only need refer here to the study of magnetism and of di-electric constant. The former has been studied by Pliicker (1857) and by Henrichsen (1888) who found that all the organic com- pounds he examined were diamagnetic and that the property was mainly additive, although the ethylenic linking, — C : C — , exerted abnormal influence. Jager and St. Meyer (1897) examined the magnetism of elements in compounds, more particularly those of chromium, iron, and manganese. Measurements of di-electric constant have been carried out by Silow (1875) by the electrometer, by Nernst (1893) by the condenser method, and by Drude (1897) by means of stationary electric waves. The latter physicist and Walden (1906) have carried out extensive work on the di-electric constants of many organic compounds. Kahlenberg (1903) showed that the dis- sociating power of a solvent upon electrolytes was connected with the dielectric constant. Thermal properties (specific heat, etc.) will be considered in § 9 of this chapter. THE HISTORY OF PHYSICAL CHEMISTRY 185 § 7. Relation of Physical Properties to Chemical Constitution : (c) Optical — The history of optical activity having already received attention (p. in), we will pass on to that of— (a) Refractive Power. — The property of refraction of light, known to physicists for a very long time, has more recently been found to be one of the most useful physical guides to chemical constitution. The earlier workers from a chemical standpoint include Cahours and Deville ; the first formula for molecular refractive power \—r(n — 1)) was put forward by Gladstone and Dale in 1858 (Landolt, 1864); a second and /M «2 - 1\ more correct expression ( — . -5 s I was deduced theoretic- \d ri* + 2/ ally and confirmed practically by Lorenz and Lorentz in 1880. Since 1880 the most prominent, but by no means the only, worker in the field has been Briihl, who has shown that the property is sufficiently additive to admit of calculation, since the constitutive influences are so regular that numerical values may in general be assigned to them. When, however, two unsaturated groups occur side by side in the molecule anom- alous refractivities are observed, and this is accounted for by Briihl as being due to the " conjugation " of two groups rich in residual affinity. Briihl has also been a notable worker in connexion with molecular dispersion of light, a property found to be more constitutive than refractive power. (b) Magnetic Rotation. — In 1846 Faraday discovered that any transparent substance in a magnetic field deflects the plane of vibration of polarized light. This property has been very thoroughly studied by Sir W. H. Perkin, who defined specific and molecular magnetic rotatory power, and found the property to be mainly additive, but in a small degree constitutive, and showing anomalous values in the case of conjugated unsaturated systems. There have been few other prominent workers in 186 A SHORT HISTORY OF CHEMISTRY this section, but we may refer to Jahn's study of the additive properties of the magnetic rotatory powers of ions (1891). (c) Spectroscopy. — As long ago as the middle of the eighteenth century the distinction of sodium from potassium salts by means of their flame-colorations was known to Marggraf and to Scheele, but more systematic examination of the spectrum was entered upon by Wollaston (1802), Herschel (1822), and others. The spectra of coloured flames were also studied by Miller (1845), Swan (1856), and others, but it was not till 1859 that Kirchhoff and Bunsen established the law that each chemical element has its own characteristic spectrum. From that time the discovery of new elements by the spectroscope has been effected by Bunsen, Crookes, Lockyer, Ramsay, and others, while various types of emission spectra (spark, arc, and phos- phorescent) have been pressed into service. In 1863 Roscoe and Clifton discussed the alteration of the spectrum of a sub- stance by varying physical conditions and by change of consti- tution. On the other hand, mathematical relations of the spectral lines were sought for by Stoney (1871), Maxwell (1875), Lecoq de Boisbaudran (1889), and Rowland (1893-), and the regular formation of some elementary spectra began to appear evident. In 1885 Balmer produced a formula by which to calculate the hydrogen spectrum, and in 1891 Kayser and Runge gave similar expressions, but not quite so successfully, for some of the metals. Twelve years later Riecke suggested an analogy between the lines of a spectrum and the harmonic vibrations of sound, and in 1 906 Stark by an extension of the idea conceived the lines as the expression of electronic vibration and deduced various electronic " atomic " formulae therefrom. Such, briefly, is the development of our knowledge of the con- stitution of spectra — a line of research which by co-ordinating optical properties with the electronic theory of matter may possibly in course of time furnish an explanation of the inter- dependence of physical properties and chemical constitution. Another equally fruitful field has been found in absorption THE HISTORY OF PHYSICAL CHEMISTRY 187 spectra. Wollaston (1802) and Fraunhofer (1814) noticed the first case of this in examining the solar spectrum, and with their work as basis, astronomy has been able to determine the qualitative composition of many of the stars and planets. The absorption spectra of solutions of electrolytes and of organic compounds have engaged numerous chemists, of whom we have only space to mention a few. Ostwald and others have shown that in dilute solutions each ion has its own definite spectrum. The work on organic compounds concerns more particularly the ultra-violet, invisible part of the spectrum, and has been carried out by Kriiss (1883-8), Vogel (1891), Hartley and Dobbie (1899), Baly and co-workers (1905), and many others. Most of the research has been done in endeavours to follow constitutional change by means of the property. An interesting practical application is that made by Witt (1876), Nietzski (1879), and others, who have based theories of colouring and dyeing upon their observations. Witt introduced the conception of chromophores or colour-producing groups and chromogens or groups which must be attached to a chromophore before the characteristic colour is exhibited. Schiitze (1892) traced a connexion between colour and increasing molecular weight. (d) Fluorescence has been found to be almost as constitutive a property as absorption spectra or optical activity. Notable names in connexion with this property are R. Meyer (1897), KaufTmann, and Kehrmann. Kauffmann applied to fluorescence a similar explanation (of " fluorophores " and " fluorogens ") to that of colour given by Witt, and, further, has found a relation between the property and the disposition of " partial valencies," while Hewitt (1900) has observed that in very many cases fluorescence is accompanied by a possibility of " double sym- metrical " tautomerism in the molecule, and suggests that the phenomenon is connected with molecular vibration due to such dynamic isomerism. § 8. Photo-chemistry — The chemical action of the ultra- i88 A SHORT HISTORY OF CHEMISTRY violet rays of light is important both in its connexion with modern theory and in its practical applications in the direction of photography, etc. Dealing with the latter aspect first, it would seem as though the darkening of silver salts was known to Boyle (who set it down to atmospheric influences), while Schultze a few years later declared the effect to be produced by light. Scheele examined the effect of the solar spectrum in detail and found the action to be concentrated in the violet part, and, finally, Ritter in 1801 ascribed it to the ultra-violet rays. The development of photography, after its initiation by Daguerre and Talbot in 1839, was especially furthered by Niepce (collodion films, 1847), Bennett (bro mo-gelatine films, 1878), and Lippmann (colour photography, 1892). In the meantime other actinic chemical reactions were brought to light, especially by Davy and Faraday (union of CO and C12 ; H2 and C12 ; chlorination of marsh-gas, etc.), and a de- tailed study of the mechanism of the process was made by Bunsen and Roscoe (1857). Their results showed that such actions were supported by certain light-waves in the ultra- violet region, which in this way supplied the necessary energy for the change. That energy was given up by the waves in question followed from the fact that a given stream of the rays lost all capacity for chemical action after passing through, for example, a mixture of hydrogen and chlorine {photo-chemical extinction). It was also noticed that the action of light usually commenced very sluggishly and then rose to a maximum {photo-chemical induction) ; this was explained subsequently on the hypothesis that an intermediate product was first formed which was itself responsible for the final more rapid rate of change. (Burgess and Chapman, 1904, and Wildemann, 1902.) A similar prin- ciple to this (the " latent action " of light) forms the basis of the developing process, which has been explained as being set up by the particles of metallic silver or of silver sub- halide (Luther, 1899) produced in the first momentary ex- THE HISTORY OF PHYSICAL CHEMISTRY 189 posure. Subsequent improvements in developing, toning, fixing, etc., have followed as new organic reagents suitable to these purposes have been synthesized. Other more recent examples of actinic action are the decom- position of various acids (succinic, tartaric, etc.) by sunlight into carbon dioxide and simpler acids in presence of uranium oxide (see Kamp, 1893), and the synthesis of indigo from an ethereal solution of benzal-0-nitroacetophenone in sunlight (Engler and Dorant, 1895). § 9. Thermo-chemistry — We have to deal here mainly with the relations to chemistry of specific heat, latent heat, and heat of reaction. (a) Specific Heat of Gases, — Measurements of the specific heat of a gas at constant pressure were made by Delaroche in 1811, but more accurately by Regnault (1853) and Wiedemann (1876). Regnault's method is the most important for the value at con- stant volume. The difference in the values (Cp - Cv = i '99) has been used by physicists (e.g. Mayer, 1842) to determine the mechanical equivalent of heat, but to chemists the ratio Cp : Cv is more interesting, since this has been proved to furnish an indication of the molecular complexity of the gas in question. Methods for the direct measurement of the ratio are due to Clement and Desormes (adiabatic expansion, 1815) and to Kundt and Warburg (ratio of sound wave-lengths in the experimental and in a known gas, 1876). The most famous applications of this formula are for the monatomic gases mer- cury (vapour), and helium, argon, and their congeners. Measurements of the specific heat of gases at high temperatures show that their heat-capacity remains constant up to 2700° C. (Le Chatelier, 1881; Berthelot and Vieille, 1884). (fr) Specific Heat of Elements and Compounds, — In 1818, Dulong and Petit proved, though not very accurately, that " the capacity for heat of many atoms is the same," namely, spec, heat x atomic weight = 6*3 ; this rule was seized upon by Berzelius as a method of 1 9o A SHORT HISTORY OF CHEMISTRY checking atomic weights — a sphere in which it has proved exceedingly useful, although at first more credence was given to deductions from isomorphism than from specific-atomic heat. Neumann educed a similar rule for compounds in 1831, and a possibility of removing some of the discrepancies of the Dulong- Petit law appeared when Regnault (1840), Kopp (1864) and others showed that specific heat in many cases varied markedly with temperature. Remeasurement of anomal- ous values such as those for boron, beryllium, silicon and carbon, over an extended upward range of temperature has, in the hands of Weber (1875), Nilsen and Pettersen (1880), and Tilden (1905), led to the verification, within narrow limits, of the Dulong-Petit law. We must also mention work on the specific heat of liquids and liquid mixtures, undertaken with a view to finding structural influences ; this has, however, not received so much attention as in the case of some other properties. ( G. F. (1703-70). Taught Lavoisier and Proust. Defined neutral, acidic, and basic salts (1744); discovered urea (1737), sulphuretted hydrogen and other compounds. Marggraf, A. S. (1709-82), pupil of Stahl and German professor. Noted increase in weight on oxidation of APPENDIX A 211 phosphorus; discovered beet-sugar (1747), alumina (as distinct from lime, 1754), and introduced the microscope into analysis ; estimated silver as chloride and knew the flame tests for the alkalies. " Black, Joseph (1728-99), Scottish professor. Worked at latent heat (1762), specific heat, thermometry, calorimetry, and elucidated nature of CaO, MgO, NaOH and their car- bonates. Supported Lavoisier's oxygen theory in preference to that of phlogiston. *"£ergtnann, T. (1735-84), Swedish professor. Important for his views on chemical affinity (1777), development of mineral analysis (blowpipe, systematic tests, gravimetric methods for Ca, H2SO4, Pb, etc.), discovery of molyb- denum and tungsten, 1778, and theory of "vital force" for organic compounds. Scheele, C. W. (1742-86), Swedish apothecary. Pioneer in nearly every branch of chemistry, with great power of observation. Discovered, amongst other substances, oxygen (1774), chlorine, manganese (1778), barium (dis- tinct from lime), phosphoric acid in bones, fluorine, hydro- gen persulphide, arsine ; and in organic chemistry, glycerol (1779), aldehyde (1774), and tartaric (1769), uric and oxalic (1776), lactic and pyromucic (i78o),prussic (1782), malic (1785), pyrogallic (1786), and citric acids ; improved qualitative analysis, developed actinic and pneumatic chemistry, etc. A confirmed phlogistonist. Priestley ', Joseph (1733-1804), theologian and chemist. Staunch upholder of the phlogistic theory. Lived at Birmingham and subsequently died in America. Im- mensely enriched pneumatic chemistry ; ' used mercury for collecting gases, invented the pneumatic trough ; discovered ammonia gas, nitrous and nitric oxides, oxygen (1774); isolated SO2 ; showed that burning organic bodies pro- duced carbonic acid ; regarded hydrogen as " phlogiston ". Richter, J, B. (i 762-1807). Invented the term " stoichiometry," and exactly determined the equivalents of various com- pounds, especially in reactions of " double decomposi- tion ". Obscured the value of his results by expressing them phlogistically. Cavendish^ Henry (1731-1810), English philosopher. In- 2i2 A SHORT HISTORY OF CHEMISTRY vented eudiometry and studied the volumetric composition of water, nitric acid, air, etc. Discovered hydrogen (1773) > estimated the density and weight of the earth ; like Priestley and Scheele, in spite of his own anti-phlogistic work, he always subscribed to the phlogistic theory. MODERN (FUNDAMENTAL) PERIOD Lavoisier, Antoine (1743-1794), mathematician, physicist, and chemist. Great politician ; " Fermier- General ". Mur- dered by the French Revolutionary Court. Insisted on accurate measurements and attention to the weights of reacting substances. Showed that metal " calces " were heavier than the metals producing them (1772); proved the " conservation of matter " (1774) ; investigated oxida- tion of P, S (i772),\Sn (1774), Hg, etc. (1775); replaced "phlogiston" by "oxygen" (1777); systematized the terms acid, base, organic compound, salt, etc. Devised the combustion process for analyzing organic substances. Improved gas-analysis ; gave hydrogen and oxygen their present names; quantitatively synthesized water (1783); damaged his reputation by trying to rob Priestley and Cavendish of the merit of their respective discoveries of oxygen and the compound nature of water. - Morveau, G. de (1733-1816), Professor at Ecole polytechnique, Paris, and friend of Lavoisier. Introduced the first syste- matic nomenclature for chemical substances, 1782 ; showed that soda-crystals could be made from Glauber's salt by heating with coke and iron. Berthollet, C L. Count (1748-1822), Professor in Paris. Chemist under Napoleon in Italy and Egypt. Renounced the phlogiston theory in 1785; investigated ammonia, prussic acid, sulphuretted hydrogen, and chlorine (" oxy- muriatic gas ") ; used sodium hypochlorite solution as bleaching agent ("Eau de Javelle," 1800) ; believed mass to be the predominant factor in chemical change, 1801 ; controversy with Proust on the law of multiple propor- tions, 1801-7. 'l 'Proust, J. L. (1755-1826), Parisian apothecary and later pro- fessor in Spain. Noted for his work just mentioned, in APPENDIX A 213 which by means of basic copper carbonates, oxides of tin and iron, and sulphides of iron, he established the law of multiple proportions. Also worked at organic chemistry. ' Fourcroy, A. F. (1755-1800), Professor in Paris. Advanced animal and mineral chemistry. (•Vauquelint L. N. (1763-1829), Professor in Paris. Discovered various elements (Be, and Cr, 1797), many naturally- occurring organic compounds (asparagine, 1805 ; cam- phoric and quinic acids, etc.), and cyanic acid (1818). i W. H. (1766-1829), English physicist and chemist. Worked at emission and absorption spectra (1802), dis- covered some of the platinum metals (1803-4), some organic substances (cystine), and regarded Dalton's atoms as "equivalents" only (1814). i M. H, (1743-1821), first Professor of chemistry at Berlin. Discovered strontium (1790), zirconium, tel- lurium (1798), uranium and cerium (1803), composition of honeystone (aluminium mellitate, 1799). Improved mineral analytical methods considerably. Dalton^John (i 766-1844), Teacher at Manchester. Discovered colour-blindness (1793), composition of carbon dioxide (1803), and olefiant gas, etc., law of partial pressures (1807), an<3 enunciated his atomic theory (1807-8); in- vented a system of elementary symbols. Davy, Sir H. (1778-1829), English chemist. Worked at nitrous oxide and phosphorus pentachloride (1800) ; iso- lated electrolytically the metals of the alkalies (1807) and alkaline earths (1808); electro-chemical theory, 1807; elementary nature of chlorine (1810); chlorine oxides, complex acids, miners' safety-lamp, chemistry of flame and actinometry. Gav-Lussac, J. L. (1778-1850), Professor at Paris. Taught by Berthollet. Worked at inorganic chemistry (halides of nitrogen and phosphorus, etc., 1800) ; gas analysis and physical research (1801-8) ; law of volumes, 1808 ; chlorine, 1810; introduced copper oxide in the combustion pro- cess, 1815 ; complex inorganic acids, 1815-20; cyanogen, 1815-22; invented volumetric analysis (acid and alkali- metry, silver, chlorine, 1824-32); improved manufacture of oxalic (1829) and sulphuric acids (1827). 2i4 A SHORT HISTORY OF CHEMISTRY Prout, y[, English physician. Supposed all atoms to be poly- mers of hydrogen, 1815. Also worked at organic products of the metabolism. Berzelius.J.J. Baron^*]*]^- 1 848), Swedish apothecary, professor (1802) and secretary (1818) to the Stockholm Academy of Sciences. His chief aim was the final establishment of the laws of chemical proportion, including the determination of atomic weights and the constitution of inorganic and organic compounds. Discovered cerium (1803), selenium (1817), thorium (1828), isolated Si (1810), Zr (1824), Ti (1825) ; worked at many inorganic compounds, notably those of the rarer metals, such as Ti, Zr, Th, Cr, Mo, W, U, V, etc. Elaborated what is practically the present system of nomenclature and symbols for inorganic compounds in 1811, put forward his electro-chemical (dualistic) theory in 1812, and extended it in 1819; drew up a table of atomic weights in 1817, and a modified one in 1826; discovered sarcolactic (1807), racemic (1832), and pyruvic acids (1835) as well as many other organic compounds ; defined iso-, poly- and meta-merism, 1831 ; contact theory of fermentation, 1834; vastly improved analytical methods and general manipulation (introduced use of rubber tubing, water baths, gravimetric filter-papers, borax, cobalt, and other blowpipe reagents,^etc.). Dulong) P. L. (1785-1838), Director of Ecole polytechnique, Paris. Worked on oxides of nitrogen (1816) and the reduced oxy-acids of phosphorus (1818) ; discovered con- stancy of specific atomic heats (1821). Mitscherlich, E. (1794-1863), Professor at Berlin (1821-63). Discovered isomorphism (1819) and polymorphism (1821). Investigated substitution (benzene sulphonic acid, 1833; nitrobenzene, 1834), benzene from benzoic acid (1834), the oxides of manganese, lactic acids, and the allotropes of sulphur (1852). Put forward a contact theory of fer- mentation (1836), and ascribed the formation of ether from alcohol to catalysis. Thhmrd, L. J. (1777-1857), Professor at Ecole polytechnique, Paris. Worked at first in conjunction with Gay-Lussac on processes for manufacturing bleaching-powder (i 799), white lead (1801), and chlorine (1810), discovered H2O2 (1818), APPENDIX A 215 HF, phosphorus hydrides and preparation of organic phosphines (1845-8). MODERN (STATIC STRUCTURAL) PERIOD (a) General and Physical Faraday, Michael (1791-1867), Assistant to Sir Humphrey Davy, and later his successor at the Royal Institution. Discovered liquefaction of gases, 1823 ; butylene and benzene, 1825; actinometry ; laws of electrolysis, 1833; discovered magnetic rotation of polarized light, 1846. Regnault, H. V. (1810-78), Professor at Aix-la-Chapelle and Paris. Worked on the composition of various alkaloids (1840 and 1860) ; established the constitution of piperine, 1863; aliphatic sulphonic acids, 1840; put forward the theory of " mechanical organic types " ; variation of spe- cific heat with temperature, 1840 ; measurements of densities (1845) and specific heats (Cp and Cv, 1853) of gases. Deville, H. St. Clair (1818-81), Professor at Paris. Investi- gated inorganic compounds (N2O5, 1849; halides of B, Si, etc. ; preparation of metals from their chlorides heated with sodium ; purification of the platinum metals, 1805-9) and physical properties (refractive index, 1854 ; dissocia- tion on heating, 1857). Pasteur, Louis (1822-95), Professor at Strassburg. Investigated optical activity (enantiomorphous sodium ammonium tar- trate crystals, 1850; resolution of racemates by mechani- cal means, 1850 ; by fractional crystallization with active base or acid, 1853 ; by bacteria, 1860; isogonism, 1861) and biochemistry (vitalistic fermentation theory, 1855 ; bacteriology, 1865-95; Institut Pasteur at Paris opened, 1889). Kopp, H. (1817-92), Professor at Giessen. Pupil of Liebig. Worked chiefly on specific volumes (1842-1855), boiling- points (1845-60), and variation of specific heat with temperature (1865). Cannizzaro, S., Italian .professor. Faraday lecture, 1872. Established rules Jor* determining which multiple of the 3i6 A SHORT HISTORY OF CHEMISTRY equivalent is the atomic weight, 1858. Other work mainly organic. TJwmsen,J. (1826-1908), Danish professor (Copenhagen). Ex- tremely thorough and varied thermo-chemical investigations (1853-1908). Berthelot, M. (1827-1907), Parisian professor and Secretary of State ; chemical historian. His work embraces four periods: (a) 1850-60, constitution and synthesis of poly- atomic fatty alcohols and acids; (b] 1861-69, pyrogenetic and electric arc syntheses of hydrocarbons (acetylene, benzene, etc.) ; reduction to hydrocarbons by hydriodic acid; (<:) 1869-85, extensive thermo-chemical investiga- tions, especially dealing with explosives; silent electric discharge syntheses ; (d) 1885-1907, agricultural and his- torical chemistry. Gladstone, f. H. (1827-1902), President Chemical Society ^ 1877 . Refractive index of elements and specific refractive index, 1858; atomic weights, refraction and dispersion investi- gations, 1860-1902. Landolt, H., Professor at Berlin. Organic As and Sb compounds, 1853; formula for refractive index, 1864; connexion be- tween refractive index and periodic law; optical activity of electrolytes, 1863; conservation of matter re-proved, 1893-1908. Meyer, J. Lothar (1830-95), Professor at Karlsruhe and Tu- bingen. Chemistry of blood, 1857; molecular volumes and periodic system, 1867-70 ; compounds of halogens with each other, 1877-85. Mendelejew, D. I. (1834-1907), Professor at St. Petersburg, 1865. Work on expansion of liquids, 1861 ; periodic system, 1869; critical data of gases, 1870-85 ; voluminous author. Horstmann, A. Thermo-dynamics of law of mass action, 1869- 7 7 ; stated the simple gas equation PV = RT ; specific volumes (1886-88). (b) Inorganic Balard, M. (1802-76). Discovered bromine, 1826; constitu- tion of bleaching-powder, 1835. APPENDIX A 217 Graham, T. (1805-69), Professor at Glasgow and University College, London. President Chemical Society, 1841. Polybasicity of phosphoric and arsenic acids, 1 833 ; dif- fusion, dialysis, and osmosis (of liquids) and diffusion and effusion (of gases), 1851 ; definition of crystalloids and colloids, 1862. Rose, H. (1795-1864), Professor at Berlin. Hydrolysis of strong acids, 1848 ; cobalt ammonia salts, columbium (discovered 1846); mineral syntheses and improved ana- lytical methods. Stas,f. S. (1813-91), Professor at Brussels. Very exact de- terminations of atomic weights, 1840-70; toxicological tests, 1850; spectra of alkaline earths, 1880. Marignac,f. C. G. (1817-94), Professor at Geneva. Constitu- tion of ozone ; thermo-chemistry and atomic-weight esti- mations (1842-83). Roscoe, Sir H., Professor at Manchester. President Chemical Society, 1880. Complex inorganic acids; isolation and compounds of W, V, etc., 1867; actinometry, 1857; spectroscopic work, 1863 ; atomic weights, etc. Winkler, C. (1838-1904), Professor at Freiburg. Gas-analy- sis ; hydraulic cements ; contact-process for H2SO4, 1875 ; discovery of germanium, 1886; atomic weights, etc. Boisbaudran, Lecoq de, Professor at Paris. Discovered Ga, 1875; Sm, 1879; Dy, 1886; Gd, 1889; mathematical relations of spectra, 1889. Nilson,L* F, (1840-99), Professor at Stockholm. Discovered Sc, 1879; atomic weights (Be, Th, Sc, 1880-2); specific heats (Dulong-Petit Law) and vapour densities at high temperatures, 1880-9. (c) Organic Dobereiner, J. IV. (1780-1849), Professor at Jena. Relation of acetic and oxalic acids to alcohol, 1821 ; noted series of "triads" in the metals (e.g. Ca, Sr, Ba, 1829); dis- covered furfurol, 1831 ; worked on aldehyde, 1834. Dumas, J. B. A. (1800-84), Apothecary at Geneva and later professor at Paris. Vapour-density estimation, 1827; etherin theory, 1828; estimation of organic nitro- 2i8 A SHORT HISTORY OF CHEMISTRY gen, 1830; cinnamyl derivatives, 1834; substitution, 1834 ; hydrolysis of nitriles to acids and amines, 1847 ; atomic weights (1856-9) ; compositions of terpenes, etc. Liebig, f. von Baron (1803-73), Professor at Giessen (1824), Munich (1852). Chief work : on fulminates with Gay- Lussac (1821), synthesis of urea (1828), chloroform (1831), on radicle "benzoyl" (1832), first radicle theory (1832), in conjunction with Wohler; polybasicity of acids (1839); vibration theory of fermentation (1839); investi- gated many other organic reactions and compounds during the next twenty years, especially among the alkaloids (1837-41) and animal products such as amino-acids and amides (1846-52); in later years became more of a physiologist than a chemist. Wohler, F. (1800-82), Professor at Gottingen (1836). Be- sides his work with Liebig, he isolated Be, Al, B and Si (1828); discovered amygdalin (1837), parabanic acid (1838), hydroquinone (1848), calcium carbide (1862), etc. ; worked on metallic sub- and per-oxides, non-metallic hydrides and halides, and pointed out the analogy of silicon to carbon in organic compounds (1863). Laurent, A. (1807-53), Professor at Bordeaux. Discovered anthracene (1832), anthraquinone (1835), phthalic acid (1836), adipic acid (1837), piperine (1840), etc. " Nucleus theory," 1837; definition of equivalent, atom, molecule, 1843 5 ether and alcohol correspond to oxide and hydrate, 1846. Gerhardt, C. (1816-56), Professor at Montpellier and Strass- burg. Theory of residues, 1839; of four types, 1853; atomic weight system ; homologous series, 1 844 ; dis- covered quinoline (1842), the anilides (1845), acid chlorides from POC13 (1851) and acid anhydrides (1852). Peltgot, E. M. (1811-90), Professor at Paris. Worked with Dumas on " cinnamyl" (1834); used PC15 for chlorina- tion, 18364 isolated various metals of the uranium group. Pelouze, J. Worked on the terpene series (discovered borneol, 1841) ; inorganic esters of alcohol ; manufacture of plate- glass, 1856. Ca hours, — . Died in 1891. Discovered amyl alcohol, 1837 ; anisol and its derivatives, 1841 ; phellandrene, 1841 ; APPENDIX A 219 methyl salicylate (in oil of winter green), 1843 ; prepara- tion of acid chlorides by PC15, 1846; allyl alcohol, 1856; tintetraethyl, 1860; alkyl sulphonium bases, 1865. Piria, ^?., Professor in Italy. Discovered salicin (1839) and worked out the chief salicyl derivatives ; sulphonation by ammonium sulphite (1850); and estimation of organic halogens in the dry way (1879). Zinin, N. (died 1880), Professor at St. Petersburg. Aniline from nitrobenzene by ammonium sulphide, 1841 ; a-naphthylamine, 1842 ; benzidine from nitro-benzene, 1845 ; azoxybenzene, 1853. Anderson, T., Professor at Glasgow. Discovered pyridine in bone-oil, 1846; constitution of piperine, 1850; prepara- tion of pyrrol, 1858; constitution of anthraquinone, 1861. Kolle, H. (1818-84), Professor at Marburg (1851) and Leipzig (1865). Synthesis of acetic acid, 1842 ; methyl sulphonic acid, 1845; electrolysis of fatty acids, 1850; nature of valency, 1854-65 ; synthesis of salicylic acid (from phenol), 1860; taurine, 1862; malonic acid, 1864 ; aliphatic nitro- compounds, 1872. Hofmann\ A. W. von (1818-92), Professor at College of Che- mistry, London (1845) ; Berlin (1865). President of Che- mical Society, 1861 ; founded the Deutschen Chemischen Gesellschaft, 1868. Amines from ammonia and alkyl iodides, 1850; constitution of aniline, 1843; alkylanilines by alkylation, 1872; isonitriles from chloroform and amines, 1866 ; myrosin and mustard oil constitution, 1868 ; vapour density method, 1868 ; discovered hydrazobenzene, 1863 ; diphenylamine, 1864 ; formaldehyde, 1868, etc. etc. Pre- pared numerous dyes (chrysaniline, 1862,' alkyl rosanilines, 1867-75 ; magdalared, 1869 ; chrysoidine, 1877), improved methods of organic preparation and analysis, etc. Wurtz, C. A. (1817-84), Professor in Paris. Wrote several noted chemical books ; discovered POC13, 1847; ethylene oxide, 1859 ; reaction of amine-formation from alkyl iso- cyanates, 1848 ; action of sodium on alkyl halides, 1855 ; reduction of aldehydes to alcohols, 1866; and the aldol condensation, 1872. jFrankland, Sir E. (1825-99), Professor in Manchester and London. President Chemical Society, 1871. Worked on 220 A SHORT HISTORY OF CHEMISTRY metallo-organic compounds, 1849-64 ; theory of atomicity (valency), 1853-60 ; hydrocarbons from zinc alkyls, 1849; constitution of acetoacetic ester, 1864; helped to devise the modern structure notation, 1867. Strecker, A. (1822-71), Professor at Wiirzburg. Chief work on amino-acid or peptide derivatives. Syntheses of ammo- acids from 1860 ; worked on the constitution of guanine, caffeine, quinine, etc. ; introduced the method of ester- preparation from alkyl halide and silver salts of organic acids, 1 86 1. Williamson, A. W. (1824-1904), Professor at University Col- lege, London. Formation and constitution of the ethers, 1850-52 ; synthesis of glycol, 1854 ; formation of aldehydes and ketones by distillation of calcium salts. Debut) H., Lecturer at Guy's Hospital. Thorough researches on the oxidation of alcohol (1856) and the composition of gases evolved from explosives. Perkin, Sir W. H. (1838-1907), President of the Chemical Society, 1883 ; oxidation of aniline and production of mauve, the first coal-tar dye, 1856; synthesis of tartaric acid, 1861 ; ofcoumarin, 1865 ; of cinnamic acid (" Parkin's reaction"), 1875; constitution of salicin, 1868; relation between magnetic rotatory power and chemical constitu- tion, 1892-1907. Kekule> A. (1829-96), Professor at Geneva (1858) ; Bonn (1865). Added the methane type to the four types of Gerhardt, 1857 ; tetravalency of carbon, 1858 (shared with Couper) ; benzene theory, 1867; azo-formula for diazo- salts, 1867 ; possible oscillation of the fourth valency in the benzene ring, 1872 ; syntheses of acetylene (from fumaric acid electrolysis, 1864), benzoic acid (Na + CO2 -f C6H5Br, 1866), crotonaldehyde and triphenylmethane, 1872. Bunsen, R. W. (1811-99), Professor at Marburg (1838), Breslau, and Heidelberg (1858). Investigated cacodyl (As(CH3)2) compounds, 1837-43 ; production of cyanides from alkalies and coal, 1847 ; method for iodine titration, 1853; actinometry, 1857; distinctive emission spectra of each element, 1859; discovery of rubidium and caesium, 1 86 1 ; invented many practical devices, e.g. his gas-burner, thermostats, water pumps, etc. etc. APPENDIX A 221 Blomstrand, C. W. ( 1 8 2 6-9 7 ) . Constancy of valency, 1860-65; complex metallammines ; "diazonium formula" for diazo- salts, 1875. Butkrow, A. M. (1828-86), Professor at St. Petersburg. First synthetic hexoses " methyleneitan," 1861 ; production of tertiary alcohols from zinc alkyls and acid chlorides, 1864; isomeric butylenes and tautomerism, 1877. Friedel) C. (1832-99), Professor at Paris. Synthesis of min- erals ; reduction of ketones to secondary alcohols, 1862 ; silicon tetra alkyls, 1863 ; action of aluminium chloride on aromatic hydrocarbons with alkyl halides, 1877. Fittig, R. (1835-), Professor at Tubingen. Discovered pina- cone reaction, 1858 ; action of sodium on mixed anyl and alkyl halides, 1863; synthesis of mesitylene, 1868; of ketonic esters by zinc dust and chlorofatty acid esters on oxalic ester, 1887; coumarone, 1883; lactones and para- conic acids (1894-1904). Griess, / P. (1829-88), Chemist at Burton-on-Trent. Dis- covered diazo-compounds, 1859-63; diazo-amidobenzene, 1862 ; diazobenzeneamide, 1866 ; Bismarck brown, 1867 ; congo yellow, 1889 ; constitution of betaines, 1867 ; orien- tation determination, 1872. Erlenmeyer, JS., sen. (died in 1909), Professor at Frankfurt. "Affinity points" cause valency, 1863; constitution of napthalene, 1866; final modern structure notation, 1867 ; synthesis of tyrosine, 1882; lactone theory, 1880; on cinnamic and iso-cinnamic acids, 1890- ; relations between isomeric fatty acids, 1898. Lossen, W. (1838-1907), Professor at Kb'nigsberg. Discovered hydroxylamine, 1865 ; stereo-isomeric imido-ethers, 1872 ; specific volumes, 1882. Saytzew, A. Sulphoxides and sulphones, 1866; first lactone (butyro-lactone), 1873; zinc dust as condensing reagent, 1875; palladium hydride, 1872. Korner, W., Professor in Italy. Formula for pyridine, 1869 ; orientation determination, 1874; synthesis of asparagine, 1887. Liebermann> C., Professor at Berlin Technical College. Action of nitrous acid on phenols and secondary amines, 1874 ; anthraquinone and oxyanthraquinones (alizarin), 1868-80; 222 A SHORT HISTORY OF CHEMISTRY constitution of anthracene and phenanthrene, 1870; quercitrin, 1879; work on azo-, alizarin-, anthracene and natural dyes. Grdbe, C., Professor at Geneva. Synthesis of alizarin, 1869; acridine, 1871; carbazole, 1872; constitution of anthra- cene and phenanthrene, -1870 ; quinoline, 1878; euxan- thone, 1880 (synthesis, 1889); on acenapthenes, 1893; condensations with 0-amidobenzophenones, 1895 ; con- stitutions of acid decomposition products of plant dyes, 1899-. Ladenburg, A., Professor at Breslau. " Prism formula " for benzene, 1869 ; equivalence of hydrogen atoms in benzene, 1874; orientation, 1875; aromatic silicon derivations, 1874; benzimidazoles, benzoxazoles and glyoxalines, 1875-8; synthesis of ptomaines, 1886; of optically-active coniine, 1886; on the constitution of atropine and other alkaloids, since 1880. Jorgensen> S. M., Professor at Copenhagen. Detection of alkaloids by polyiodides, 1870 ; constitution and properties of metallammino (cobalt) salts, 1880-1908 (controversy with Werner). Volhard, J., Professor at Halle. Synthesis of sarcosine (1862) and creatine (1869) ; thiocyanate titration for silver (1874) ; thiophenes from succinates and P2S3 (1885). Nietzski, R.y Professor at Basel. Aniline black, 1876; pre- paration of quinones, 1877 ; theory of colouring matters, 1879 ; Biebrich scarlet, 1880 ; hexaoxybenzene compounds, 1885. MODERN (DYNAMIC STRUCTURAL) PERIOD (ARRANGED ALPHABETICALLY) (a) General and Physical Arrhenius, S., Professor at Stockholm. Ionic theory of elec- trolytic dissociation, 1886; hydration of ions, 1888; conductivity of pure water, 1893 ; viscosity of electrolytes, etc. Briihl, J., Professor at Heidelberg. Many investigations into the effect of constitution on refractive index, 1880- ; APPENDIX A 223 constitutions of terpene derivatives, 1890; refractivity of benzene, 1894; of tautomeric substances, 1899, etc. Dewar, Sir J., Professor at Royal Institution. President Chemical Society, 1897. Formula for quinoline, 1871 ; on liquefaction of gases, 1884- ; "vacuum vessel" for holding liquid air, etc. ; liquefaction of hydrogen, 1898 ; charcoal as gas absorbent at low temperatures, 1905. Guye, P. A., Professor at Geneva. Theory of quantitative optical rotatory power, 1890; work on "asymmetry pro- duct," 1891-9 ; atomic weights from gas-densities and de- termination of critical data, compressibilities, etc., 1900- . Nernst, W., Professor at Gottingen and Berlin. Diffusion theory of solutions, 1888; dissociation of pure water, 1894; dielectric constant determination, 1894; quadrant electrometer, 1896, etc. Ostwald, W., Professor at Leipzig. Nobel prize, 1909. Pyc- nometer and other physico-chemical apparatus, 1873- ; partition of a base between two acids (dilatometry and refractive power), 1878 ; rate of hydrolysis of salts and esters, 1883 ; conductivity of acids, 1878-87 ; various methods of comparing the relative " affinities " (affinity- constants) of acids, bases, etc., 1885- ; viscosity of solutions, 1891 ; definition of properties (additive, con- stitutive, colligative), 1891 ; conductivity of pure water, 1893. Pope, W. J., Professor at Manchester and Cambridge. Synthesis of asymmetric (optically-active) nitrogen (1899), tin (1900), sulphur (1900) and selenium (1902) com- pounds ; crystallographic theory, 1906 ; gold and platinum alkyls, 1908. Ramsay, Sir W., Professor at University College, London. Nobel prize, 1904. President of Chemical Society, 1907. Synthesis of pyridine, 1877 ; atomic weight of zinc, 1884; improved Hofmann's vapour-density method (application to varying temperatures and pressures), 1885; surface- tension and molecular weight, 1893; critical data, 1894; the rare gases, 1893-1908; radio-activity, 1903- ; de- gradation of heavy elements to lowest member of their series, 1907- ; electronic theory, 1908-9; radium emana- tion or niton, 1910. 224 A SHORT HISTORY OF CHEMISTRY jRayleigh, Lord. Nobel prize, 1904. Composition of water, 1889; re-determination of gas densities, 1892- ; dis- covery of argon, 1894; and other physical researches. Tschugaeff, Z., Professor at Moscow. Optical rotatory power in homologous series, 1898 ; effect of boiling-points of homo- logous compounds, 1894; conductivity of weak acids, 1900; amphoteric electrolytes, 1902, etc. Walden, P., Professor at Riga. Conductivity of organic acids, 1891; "Walden inversion," 1895; unsaturation and optical activity, 1896 ; conductivity of non-aqueous sol- vents, 1901-6; dielectric constants, 1906- , etc. Young, S., Professor at Dublin. Investigations on vapour- pressure, 1886-92; relation of boiling-points, molecular volumes, and other properties and chemical constitution, 1890; critical data, 1893-4; separation of mixtures by distillation, ^94-7. (b) Inorganic Crookes, Sir W. President Chemical Society, 1867. Discovered thallium, 1861 ; phenomenon of cathode rays, 1880; spec- troscopic work on rare earths since about 1880; theories of ultimate genesis of matter — "protyle," 1886; "meta- elements," 1889; fixation of nitrogen, 1892. APPENDIX A 225 Curie, M. (1859-1906) and Mme. (Professor at Paris, in her husband's place). Radioactivity of uranium and thorium minerals, 1902; isolation of radium, 1903; polonium, 1903; disintegration of radium, 1904- . M. Curie was also noted as physicist and crystallographer. Lobry de Bruyn, C. A. (1857-1904), Professor at Amsterdam. Nitro-aromatic compounds, 1890; hydroxylamine, 1891; hydrazine hydrate, 1894, (anhydrous), 1896; colloidal solutions, 1902. Moissan, H. (1852-1907), Professor at Paris. Nobel prize, 1906. Metal oxides, 1879-83 ; fluorine compounds, 1883 ; isolation of fluorine, 1886; electric furnace, 1892; metal carbides and carborundum, 1893-4 ; nitrides ; artificial diamonds ; reduction of refractory metal oxides, 1896 ; silicon hydrides, 1902. (c) Organic Anschiitz, R., Professor at Bonn. On pyrocondensatioris, 1878 ; oxidation of fumaric and maleic to racemic and mesotartaric acids, 1880 ; citraconic and isomeric acids, 1 88 1 ; aluminium chloride syntheses, 1884 ; stereoisomeric hydrazones, 1895. Armstrong. H. E., Professor at South Kensington. President of Chemical Society, 1 893. Constitution of terpenes and cam- phors, 1871-96; "centric" formula for benzene, 1892; origin of colour, 1893 ; electric conductivity and theories of solution, 1892-1902; naphthalene-sulphonic acids, 1891 ; Caro's acid, 1902. Baeyer, A. (1835-), Professor at Berlin and Munich. On polymethylenes, 1861- ; constitution of furfurol and pyrrol, 1870; indene, 1884; orientation of phthalic acids, 1871 ; reduction of benzene and benzoic acids, 1887-92 ; strain theory of carbon ring-stability, 1885 ; steric formula for benzene, 1888 ; centric formula, 1892 ; on purine de- rivatives and uric acid, 1863-70; indigo constitution and synthesis, 1866-90; terpenes, 1890-1900, etc. Bamberger, E., Professor at Munich. Guanidine and cyan- amide compounds, 1880 ; constitution of retene, 1884 ; chrysene, 1895 ; sodium and amyl alcohol as reducing 15 226 A SHORT HISTORY OF CHEMISTRY agent, 1887 ; diazo-controversy with Hantzsch, 1895- 1900. Beckmann, £., Professor at Erlangen. On iso-nitroso com- pounds, 1886 ; equivalence of nitrogen valencies, 1885 ; isomeric benzaldoxines, 1885 ; apparatus and thermometer for molecular weight by freezing-point (1888) and boiling- point methods (1889), etc. Bernthsen, A. Badische Anilin u. Soda Fabrik. Methylene- blue constitution, 1883 ; safranine, 1885 ; thiodiphenyl- amine and phenazine syntheses, 1886 ; acridihes, 1884-93 J hydrosulphurous acid, 1905. Bischoff, C. A. (1855-1908), Professor at Riga. Syntheses of aliphatic acids by ketonic esters, 1876 ; on ring-formation, 1880-88 ; stereochemistry of nitrogen atom, 1890 ; steric hindrance, 1894. Brown, A. Crum, Professor at Edinburgh. President of the Chemical Society, 1891. Contributions to modern structure rotation, 1865; thetines, 1878; quantitative hypothesis for optical rotatory power, 1891 ; electrolytic syntheses of malonic esters, 1891 ; osmotic pressure, 1900. Caro, H. Induline dyes, 1865 ; Bismarck brown, 1867 ; acri- dine synthesis, 1871; eosin, 1873; monopersulphuric acid, 1898. Claisen, L., Professor at Kiel. Aromatic ketonic esters, 1880; benzalacetone, 1881 ; pyrazole synthesis, 1888 ; /?-dike- tones, 1889 ; tautomeric substances, 1893-99. Collie, J. IV., Professor at University College, London. Action of heat on complex ammonium and phosphorium salts, 1881-1888 ; on the rare gases, 1896 ; space formula for benzene, 1897 ; pyrones, quadrivalent oxygen, poly- ketides, etc., 1891-1907 ; decomposition of CO2 by silent electric discharge, 1901. Curtius, T., Professor at Heidelberg. Diazoacetic ester, 1883 ; hydrazine, 1887 ; hydrazoic acid, 1890-93 ; pyrazo- line derivatives, 1894 ; aldazine transformations, 1900 ; glycocoll, asparagine and polypeptide syntheses, 1904. Fischer, Emil, Professor at Berlin. Constitution of rosa- niline and alkylrosanilines, 1867-75 '•> phenylhydrazine, 1875 ; phenylhydrazones, 1877 ; indol and indazoles, 1885 ; sugars, constitutions and syntheses, 1884-1900 ; glucosides, 1893 ; configuration of pentoses, hexoses, APPENDIX A 227 and tartaric acid completed, 1894 ; constitution and syntheses of the purines, 1881-1901 ; syntheses of poly- peptides, 1900; discovery of proline, 1899. Gattermann, L., Professor at Heidelberg. On nitrogen chloride, 1888 ; alkylene phenol ethers, 1889 ; liquid crystals, 1890 ; copper powder and diazo-compounds, 1890; electrolytic reduction of nitro-compounds, 1893; sulphination by diazo-compounds, 1898 ; thio-anilides, 1899; aldehydes by Grignard reagent, 1904. Hantzsch, A., Professor at Leipzig. Pyridines from aldehyde ammonia, 1882 ; coumarone syntheses, 1886 ; theory of stereo-isomeric oximes, 1890 ; phenylnitromethane and conductivity of ^-acids and ^-bases, 1896 ; hyponitrous acid, 1896. Haller, A,, Professor at Paris. Syntheses from cyano-fatty esters, 1888 ; on camphor and borneol, 1889-1906 ; con- stitution of camphoric acid, 1 893 ; partial syntheses of borneol (1891) and camphor (1895) ; effect of un- saturation (1899) and ring-formation (1905) on optical activity. Kipping, F. S., Professor at Nottingham. Hydrindene de- rivatives, 1893-1904 ; sulphonic derivatives of camphor, 1895 ; keto-hexamethylenes, 1897 ; organic silicon de- rivatives, 1904-. Knoevenagel, £., Professor at Heidelberg. Dihydroresorcinol, 1894; S-diketones, 1894; terpene syntheses, 1896; con- densation of aldehydes and malonic ester, etc., by weak bases, 1899; pyridine syntheses, 1898; moto-isomerism, 1903 ; sulphination, 1908. Rnorr, Z., Professor at Jena. Pyrazolone and antipyrine syn- theses, 1883; quinoline syntheses, 1886; pyrazole syn- thesis, 1887 ; tautomerism of methylpyrazole and of ben- zene, 1894; morphine alkaloids, 1890; tautomerism of diacylsuccinic esters, 1896- . Le Bel, J. Stereochemistry of carbon, 1874; attempts to make optically active benzene compounds, 1882 ; stereo- chemistry of nitrogen, 1891; optically active asymmetric nitrogen, 1900. Marckwald, W., Professor at Berlin. Furfurane compounds, 1888; glyoxalines, 1892; tautomerism, 1895; stereo- 228 A SHORT HISTORY OF CHEMISTRY chemistry of nitrogen, 1900; optical activity without atomic asymmetry, 1906; radio-activity, 1903- Menschutkin, N. (1842-1907), Professor at St. Petersburg. Contributions to law of mass action (velocities of ester- formation and other organic reactions ; effect of constitution on the rate of reaction). Meyer, Victor (1848-97), Professor at Heidelberg. Aliphatic nitro-compounds, nitroso-compounds and nitrols, 1872; vapour-density method, 1878 ; iso-nitroso-compounds, 1882 ; thiophene, 1883; isomeric oximes, 1883; steric hindrance, 1891-4 ; ester ifi cation and saponification "laws," 1895 ; iodoso-, iodo- and iodonium compounds, 1895. Perkin, W. H., Professor at Manchester. Berberine, 1889; tetramethylene compounds, 1894; hexamethylene syn- thesis, 1894 ; oxidation-products of camphor, 1895- 1902; braziline and haematoxylin, 1900-7; syntheses in the terpene series, 1905- ; brucine and strychnine, 1910. Thiele, J., Professor at Munich. Guanidine derivatives, 1902 ; tetrazole derivatives, 1895; nitramide, 1897; theory of " partial valencies," 1899; unsaturated lactones, 1902. Von Pechmann, H. (1850-1803), Professor at Tubingen. On anthraquinone, 1880; coumarin-syntheses, 1883; a-dike- tones, 1887 ; /-xyloquinone from diacetyl, 1889; diazo- methane, 1894; preparation of hydrazine, 1895. Wallach, O., Professor at Gottingen. Extensive work in the terpene series, 1887- Willstatter, R., Professor at Munich. Tropic acid, tropine and atropine, 1895-1903; ecgonine and cocaine, 1897- 1903; lecithin, 1904; 0-quinones, pyrones, 1905; chloro- phyll, 1907- . Wislicenus, J. (1835-1902), Professor at Wiirzburg and Leipzig. On aldehyde-ammonia condensations, 1859 ; lactic acids, 1861-1873 ; oxyacids from cyanhydrins, 1862 ; ketonic and other organic ester syntheses, 1869-82 ; alkyl- acetoacetic esters, 1883 ; stereochemistry, "Die raumliche Anordnung der Atome," 1887 ; pentamethylene syntheses, 1895. APPENDIX B IJJfil ill *" s §•* •C P - M O «i5 ^ — ' flj (U :-.! ^^ ^j u § w rt ja .B5 <" ^ g S £ 8'~ ^ S s .s g3 1 2' j3 i u • ,-1 \ -gPQ |^ c 2 S 0) ;=P .\J 3J C^ J_ *- W ^ I's-B^l ~ ^ 3^ S -S3 o W 8 S "S S S *G S c o « « <* H-35 s o-a-S.ss <** . c i OTJ .« & = -g «•§ w 5 C ^5 s 5 o3 .o ^ «° •£ -3 &§J 2 « " \E O O ^_ | W T « » 0 03 '^ 229 230 A SHORT HISTORY OF CHEMISTRY §~ £ 3 § C & 1 6 "H I I *O Cid § 1 I % m 1 ^ 1 •fi O ^ 2 ' c " § "g *d rt g 6 'o rt | is 1 1 || •^ 2 V *§ rt o 8* "o rt •g «2 « O J < III 1 1 C x M _0 rt B *lM **^ £ J9 ^ 3 C H 111 1 I 1 1 g 1 j i i 3 C 3 1 .5 Eg 3 "S 1 -d « So .y o *c ti! .r- 3 T I < 1 .g •3 T3 SB "rt n 6 X H Marggraf discovered sugar juice. Watson prepared pure platin Marggraf distinguished alun limp Black on carbonic acid and a Black discovered latent heat. Scheele isolated d-tartaric aci Scheele discovered fluorine. Scheele discovered manganes Rutherford isolated nitrogen. Koueiie discovered urea. Scheele distinguished baryta : Scheele discovered chlorine and acetaldehyde. Priestley discovered oxygen. Scheele discovered oxalic and Scheele discovered glycerine. o L i_ j: i . ,,„:„ acids. Scheele discovered prussic ac Cavendish showed that hydro to form water. « 3 ••j- Tf Wj W) m N o» H N WHO o t^ t^» r>» t*^ t^ t^ t^ !§ i t^« t^** c 0 00 M H H M M ~* APPENDIX B 231 I I 0 £ i i* I li s-s p I'D Sjg Guyton de Morveau obtained washi soda from Glauber's salt. Lavoisier : first quantitative synthe of water. Lavoisier showed alcohol and carbi dioxide result from sugarfermentatic Charles discovered law of expansion gases. Scheele isolated malic acid. Scheele discovered pyrogallol. Preparation of ethylene. ' Lampadius discovered carbon bisul phi Vauquelin discovered chromium. Klaproth obtained mellitic acid. Welter discovered picric acid. Nicholson and Carlyle : quantitati electrolysis of water. Wollaston on spectroscopy. Se"guin prepared " morphium ". Derosne isolated narcotine. Northmore liquefied chlorine. i € i 5j- U"> VQ txOO O o co oo oo co co x, tx tx tx tx t> o\ ch Ot o^ o^ ON o i H N CO 3 O O < 3 CO CO 0 $£ H M » "* H M H H A SHORT HISTORY OF CHEMISTRY E ^ 8 E bo 0 CO c CTJ S s« "s 0 5 'S T3 T3 U *^ »c C *? s' *§ ^! 3 £ 3 B s t« >> 1 « BO K*"~» u 1 : lil^g^i 2 .» -u 1 1 i -s >> 4 'M -, S -| p| ^3 *v,|J 1 1 16 rt *S ° X „• 1 1 1 § J fj g "g j5»*| 9 2% > u *- 3 O £ °Q ° °O PU £~ "^ '3 C* 3 E .2 'C p W) § 4 | | 3 k la Experimental. If 1 1 1 1 C/3 «T3 D rrt 4^ "^ ^^ 4-* rt isolated silicon, lementary nature of c i discovered cystine. ic prepared anhydrous iscovered iodine. t on solar spectrum, ic's work on cyanoger ptical activity of sug discovered lithium, icovered xanthine. c JS "3 -• c« w o " ^ £ M 0 C .S w .2 E OS-. QT3 QJ co 3 1 1 S > Q Q ||||lj ^J § n 3 ^^ _0 toO« iArfveds Marcet « i/*lVQ t^i 00 Qi O H OJ CO "^" ^^ O t^« OOO OOW M HHMM HH cfl 00 OO 00 CO CC 00 CO 00 C O 00 00 00 CO Q H M H M H H M H -f M H M H APPENDIX B 233 - 313 w S ex .« S l-M O .C I** 3 6 5 2 c 0*6 '5 S a T3 . e«|S 22 £ o -3 &S Sfi'o^ ^ 3 ^3 T3 C 5"S l§ |j! IP "8 •~! •*"* f-sl II "S ^2 „ «i!ll r^oo M t-H 00 00 M CO IN 0) 00 CO 234 A SHORT HISTORY OF CHEMISTRY w 1 IS C *•* w 12| 42 ~ ° rt O .!•- Si S2 . s.Bs II .SO 11 -1 g1 iijJli M 3 Q0Q DJ II 1 . ^ 111 I* -Si P. «ll u £ Be I 1 u "3 ^ II I-H :O I* te I -8^1 •S^s" •S:lu.2 S S-E10 c 8 s|s w 1« ^§s-s-,-§| 2 rl'o M StJ 8aga«JI 15? 0^3 SflSjgl'a-lti, IS OQQ 3 ^ .ii eg CO ro CO APPENDIX B 235 1 1 4-1 IM c w c O nj flJ 3 gj C rv ^ .2 H '§ & >> -W *§ 3 0 3"« ^B «-ig bD rtTS'Jc^O50^ 3| 1 111 Hill J JO Q C TJ w g • o 5 § .| ^ ,2 e* 1 -6 JT5 rt C 'o *O ^ S rt^5 g J3 '§ O No_..5. di^ ™ § I'll 11 || = rt oJ ttf '5 . "u-a § r; JU g ^"5, S, G,CT3J> 'S.O S S l§il ii i^ i* •2g|M.s§B 8§ •§ Illlisl s^ 1 pqm_l «OH co fa •^- i/^ O r^ oo o* o H CO ro CO CO CO CO V •<*• » 00 00 CO CO CO 00 C 0 H H H H H H H H 236 A SHORT HISTORY OF CHEMISTRY O §.§&§ §§§•§ sl^ O C£jj i) ^ "o •• O O a s '8 t Kopp commenced his wo volumes. Zinin discovered a- and amines. -4- GO TJ- 00 O IT, 00 APPENDIX B 237 i? 3 J* 11 rt 3 £ .2 1« 1 1 g ^ CQ C/3 jl illlli §3*3 Ii li 11 OP, Ifll PHQpQfe o »o 00 M 1 in 00 H m 00 H TJ- m m m oo oo M H O f^OO m m m 00 00 00 ' H H M »n oo H A SHORT HISTORY OF CHEMISTRY n cr • c/3 | | 13 & •g | O .2 S rt s -i3 I 1 *J J» c «r i £ i! a'C ^ 1 1 pq (it 9 1 1 | * Is ^ > 4} Oj 1 tl, r/3 J3 C T5 i-> ** 1-1 tC *-" OO*3 *> c s >-, o <£ .±3 <*•> .• CJ O »^ T3 ex, oJ c fj o »5 ^ JS2 "^ u <3 Tt • j| « S 2 "^ I* • 1" | 1 1 < N | g "5 g , .y 5 §^ c o3 S* &• 1 1 lll-g ii i s s -131. "&'•£ •£ °tt'a ^. Ortw c e u "( S •« tioj •SI" s ?1^^ 5 9§ 8 g 3 fi rt e^X «^Coj I w !! Ii HPl pq W pq pq Oc^c^WOPQOO fe w^OQPQ M M . OH N ro T)- 10 vi 3 1 H M H vO VO C - G l§ .2-8, sfl jiir 'C rt rt C .ti 3 e O g bDrt-P at C • — «, rt 1'SII 2.^^ Si 0) o * lg- . 'CA <^ *ri 0) 0) w •- ^•5^ S C C to C c c £ ;Sa5-S-S •S'g's s-gs |logsS I5L«4il rig S3 || ll C ft, >vc 81 ^•Sgs S 'C c .Si rt I O W 240 A SHORT HISTORY OF CHEMISTRY o . 'C 4J § 1 bC 3 C g •S 5=^ N ^ "t2 " c *2 •""" " 'O •a c c ^ « S 1 * «d .a •§, « ° 2 . Experimental. rt O N "^ "P C c S* c „; o -n c U-, p'S ^: i oo t^* t^* r** r^ ^ t^« t^ i 00 00 00 00 OO 00 OO H M M H M M M APPENDIX 541 to CL. ^i (M O CO ui rt 3 bD -^ ^ rrt O >*"~s> c o CO s ij 3 _0 § 1 13 12 si 1 8 | £* M"i « 11 i C y 3 bJO rt y •*^' -H o .C fl PO ."§ § 6 Jl •s f •§ 1s g O « co g" . g^ O 2 O § jiLsa-g^l 5gl§l2J H r/l - — g.? i.sg«tJ^ H 111115^ rt os .2 _. -5 w ^ H ., -a ti 7, b « "Illf IS c o CO 0) II 51 it bo • »-t ^) Q sf^8 Il5-a««-a O >^ ^^ ?% g'S § jS.o jg 3^B«a si C rt s« « ui ; rt X •s •S.2 »O ^ UJ V ^.s d) (^ 1 1*5 . fe« pq> g s 0 J: f A B '* 1 0 J ? h J 3 '£ « .-S'S § g o 5 S u .a *o O CJ ^ O ^ s 2 t g &£*-*.£ ^A E'S'cS | cL )S 1 |1 ;t C 2 8 C c o i j *c 1 | "8-3 M'oS t^£ ^\ o "o 0 < o PQ " ~ O " u « 6 «j .5 -H c3 ic a > M C i 15 ,2 -3^3 "3 .5 o.c -a Experimental. Ladenburg synthesized coniine. Ladenburg synthesized ptomaines. Loew obtained formose from form; hyde. Moissan isolated fluorine. Piutti discovered M O O C rt-^ i 5^ >,rrt O 2« 1 8 is O C tl >> 12 M N 8-8 ^^ C rt > 24 c oj rt c to o 2-_e • II ill §1 ffiw &QPQCQ cells. h on pheny rt rt iff; 2s S.2 flaS ving ntzsc bas £ 'V V C V & 2Z2& 0 D C X rt > >,-> 1-1 p I _c C .£ i 0 0 ; C t*H *° '"S '^^ e *j£ 1 (J ^ « 3 rt "5 rfr§ C 0 ll o JJ * P 111 hi! J H o c rt § T .£ ^ 1 jb £ 1 o B >^ c 2^ 1 'c CTl OH *r^ T^ 4J w 15 Experimental. Dewar liquefied hydrogen. E. Fischer synthesized guanine punne. Ramsay and Travers isolated i krypton, xenon. Ruff's method of sugar-synthesis. Barbier on magnesium and m iodide. Collie and I'ickle discovered oxo salts. E. Fischer discovered proline. E. Fischer synthesized caffeine. Marchlewski synthesized cane-sug Gomberg on triphenylmethyl. Grignard's reagent discovered. E. Fischer commenced work on peptides. Loeb's electrolytic reduction of i benzene. Smiles (and Pope and Peachey) resi a compound containing asymn: sulphur. E. Fischer synthesized proline. Marckwold and M'Kenzie's first a metric synthesis. Willstatter synthesized atropine. Traube synthesized uric acid, xant caffeine, etc. D iii i APPENDIX B 245 3 u 1 1 II X O rt J* 3 o ^ j i) C "(U y rt 6 g g 3 ^ be 3 - C o 2" . — . 2 03 1 1 J1^ 1 " « &, 'o *a !| « o> 1 1 2*6 3 rt C k J31 1 1 1 1 y c 1 3 w T3 C ° Jd i 1 rt »rt rt g "^ TS.^^'d • • 'y 1^ 1 § J g S § 0-J3 rt y\M <^ l«§|,g rt "o 4 PQ s ^ O li ij-i rt - ° c g 0 . V 8** 2 6 N rt O (,_, "* o rt •£ "rt ^'rt' "S.S g rt Ij *a I*H O lit w | • 1 . ' 1 a X a! X en 5^ |S^ 3s o 2 ~rt 1*9 S c2 ^ ^ 1 ** — c •^ U 'J3 en i3 >-, |S 8 i ^ *3 o ex 1:1 |§I rt o ^d -° - i-J 2 "rt *5 |I "c o III •J k _c W 13 ^S o || s <:5 S* w « s 3 t*Q W < l> ^ i H H I i 1 oo c H V- l ? INDEX OF NAMES [The figures in black type refer to the " Biographical Index of Chemists" Appendix A.] ABEGG, 55, 181, 245. Abel, 170, 171. Achard, 161, 230. Adam, 161. Aders, 150. Agricola, 65, 125, 156. Albertus Magnus, 29, 45, 65. Amagat, 173. Ampere, 62, 173. Ampere Electric Co., 163. Anaximenes, 27. Anderson, qi, 92, 123, 140, 141, 219, 236. Andreocci, 92, 135. Andrews, 72, 174, 191, 239. Angeli, 71. Anschiitz, in, 125, 198, 225. Arago, in. Archimedes, 182. Aristotle, 27. Arfvedson, 69, 232. Argand, 161. Armstrong, E. F., 145, 153, 245. Armstrong, H. E., 72, 97, 143, 225, 243- Arrhenius, 57, 61, 177, 193, 222, 242. Atkinson, 143. Atterberg, 143. Aussedot, 165. Auwers, 103. Avogadro, 35, 36, 81, 173, 179, 232. BACON, n. Badische Aniltn und Soda Fabrik, 1 60, 169, 199, 200, 226. Baeyer, 72, 91, 92, 93, 94, 95, 96, 97, 100, 102, 109, no, 118, 122 124, 125, 127, 129, 131, 135 142, 143, 148, 150, 151, 169, I7O, 183, 199, 2OO, 204, 225, 238, 239, 240, 241, 242, 243. Baker, 194, 208. Baker, Miss, 55. Balard, 62, 70, 121, 160, 216, 233. Balmer, 186, 241. Baly, 96, 105, 187, 245. Bamberger, 93, 97, in, 135, 199, 225. Barbier, 130, 142, 143, 244. Barlow, 176, 245. Barnal, 141. Barreswil, 72. Barth, 200. Bartoletti, 146. Baskerville, 165. Baumann, 130, 150, 151, 204. Baubigny, 207. Bechamp, 124, 127, 170, 199, 200. Becher, 15, 29, 152, 210. Beckett, 141. Beckmann, 54, no, 143, 181, 190, 198, 226, 242. Becquerel, 74, 243. Behrend, 151, 242. Beilstein, 119; 183, 199, 200. Benckiser, 120. Bendant, 175. Benedicks, 74. Benedikt, 201. Bennett, 188. Bergmann, 16, 45, 46, 66, 70, 77, 198, 201, 202, 211. Berkeley, Earl of, 181. Bernoulli, 173. Bernthsen, 72, 131, 134, 135, 170, 226. Bertagnini, 125, 200, 204. >47) 248 A SHORT HISTORY OF CHEMISTRY Berthelot, M., 47, 67, 72, 85, 93, 117, 118, 120, 143, 162, 170, 175, 189, 190, igi, 192, 193, 199, 216, 237, 238, 239. Berthelot, D., 173, 179. Berthollet, 19, 46, 47, 60, 160, 171, 192, 202, 212, 213, 231. Bertrand, 143. Berzelius, 3, 19, 31, 32, 35, 36, 37, 42, 46, 50, 51, 56, 60, 62, 63, 65, 66, 67, 68, 69, 70, 72, 77, 78, 79, 80, 81, 83, 84, 86, 123, 125, 126, 137, 152, 176, 189, 198, 201, 202, 203, 206, 207, 214, 232, 234- Besanez, 146. Bessemer, 156, 157, 237. Betti, 103. Bigelow, 195. Billitzer, 179. Biltz, 180, 193. Bineau, 102, 128. Biot, in, 232. Bird, 159, 243. Birkeland, 162, 245. Bischoff, 107, 115, 126, 226, 241, 242. Black, 13, 16, 17, 18, 19, 20, 62, 64, 190, 202, 211, 230. Bladin, 92. Blomstrand, 53, 54, in, 199, 221, 240. Blumlein, 134. Blumenthal, 161. Bocklitch, 151. Borodine, 200. Bottger, 199. Bottinger, 134. Bouchardat, 143, 151, 235. Boullay, 79. Boyle, 2, 7, n, 12, 13, 14, 17, 18, 23, 29, 30, 32, 34, 62, 81, 120, 160, 172, 173, 188, 201, 202, 2IO, 229. Braconnot, 124, 147, 150, 171, 233. Bradge, 157. Brand, 70. Brandt, 70. Bredig, 179, 245. Bredt, 124, 142, 143. Brieger, 151, 241, Brin, 158, 241. Brisson, 204. Brodie, 124, 238. Brown, A., 153. Brown, Crum, 88, 92, 113, 192, 226, 238, 242. Brown, H., 153. Bruce, 94. Briicke, 139, 178. Bruhl, 96, zoo, 101, 103, 142, 143, 185, 222. Brunner, 157, 159. Bruylants, 143. Bucherer, 72. Buchner, 92, 119, 153, 243. Buckton, 130. Buffon, 46. Bunsen, 67, 69, 79, 129, 130, 157, 163, 164, 170, 186, 188, 197, 198, 205, 220, 235, 237, 238. Burgess, 188. Bussy, 130. Butlerow, 104, 117, 119, 120, 144, 221, 238, 240. Buys-Ballot, 175. CADET, 129. Cagniard de la Tour, 152, 174, 233, 235- Cahours, 120, 121, 124, 125, 130, 143, 150, 185, 218. Cailletet, 174, 240. Cain, 245. Cannizzaro, 38, 120, 179, 205, 215, 237- Carius, 204. Caro, H., 72, 91, 127, 169, 170, 226, 239, 240. Caro, N., 163, 245. Carlisle, 24, 231. Carrara, 178. Castner, 157, 158, 159, 241, 242. Cavendish, 13, 16, 18, 20, 21, 23, 24, 26, 62, 197, 206, 211, 212, 230. Caventou, 140, 141, 233. Cazeneuve, 102. Champion, 171. Chance, 159. Chancel, 121. Chapman, 188. Chaptal, 19, 20, INDEX OF NAMES 249 Charles, 173, 231. Chevreul, 120, 139, 146, 162, 234. Chick, 126. Chiminello, 194. Chiozza, 200. Christensen, 65. Ciamician, 94. Claisen, 103, 122, 123, 125, 127, 135, 226, 241, 243. Clarke, 207. Classen, 202. Glaus, 70. 97, 106, 170, 239. Clausius, 56, 173, 237. Clayton, 167, 229. Clement, 189. Clerget, 204. Cleve, 73. Clifton, 186. Cock, 156. Cohen, 114, 115, 196. Cole, 150. Collie, 91, 96,99, 100, 125, 143, 203, 226, 243, 244, 245. Combes, 123. Conrad, 124, 126, 240. Constan, 72. Coppet, i8r. Cort, 156, 231. Cosak, 199. Couper, 87, 88, 89, 220, 237. Courtois, 70, 168, 232. Crafts, 118, 130, 198, 239, 243. Cramer, 150. Crawford, 65. Crew, 65, 69. Croll, 65. Cronstedt, 70, 201. Crookes, 43, 69, 73, 162, 186, 224, 238, 242. Crossley, 119. Curie, 74, 75, 175, 194, 225, 245. Curtius, 71, 128, 147, 226, 241. DAGUERRE, 188. Daimler, 122. Dale, 169, 185, 237. Dalton, 3, 19, 32, 33, 34, 35, 41, 49, 66, 77, 87, 173, 205, 206, 213, 232. Daniell, 51. Davy, E,, 117, 235. Davy, Sir H., 3, 19, 30, 35, 46, 49, 50, 56, 61, 62, 69, 71, 73, 76, 157, 166, 190, 213, 215, 232. Davy-Henault, 192. Deacon, 158, 241. Debierne, 75. Debray, 70, 156. Debus, 92, 121, 123, 125, 170, 199, 220. De Hemptinne, 163. De la Rive, 156, 235. De la Roche, 189. D'Elhujar, 70. Delisle, 203. Del Rio, 70. Demarsay, 73. Democritus, 28. De Nehan, 164. Dennstedt, 203. Derosne, 141, 231. Desch, 105. Desfontaines, 114. Designolles, 171. Desormes, 189. Dessaignes, 124, 125, 139, 150. Deville, 70, 71, 72, 143, 156, 157, 174, 175, 185, 215, 237. De Vries, 180. Dewar, 22, 91, 150, 174, 223, 239, 244. Dickinson, 165. Diehl, 122. Diels, 126. Diesbach, 168. Dimroth, 128. Dioscorides, 198. Divers, 71. Dixon, 194. Dobbie, 187. Dodge, 143. Dobereiner, 38, 71, 92, 123, 125,217, 234- Dobner, 169. Don Antonio de Ulloa, 70. Donnan, 194. Dorant, 189. Douglas, 156. Dowson, 163, 166. Drechsel, 125. Dreher, 130. Drewson, 169, 250 A SHORT HISTORY OF CHEMISTRY Drude, 184. Dubrunfaut, 146. Duhamel, 6g, 229. Dulong, 3, 36, 71, 72, 189, 190, 206, 214, 217, 233. Dumas, 37, 39, 42, 50, 51, 79, 80, 82, 86, 93, 120, 121, 122, 124, 125, 143, 166, 179, 199, 200, 203, 206, 207, 217, 218, 233, 234, 235, 236. Dunstan, A. E., 183, 196. Dunstan, W. R., 146. Duppa, 124, 125, 150, 200, 237. Dutrochet, 137. Dyar, 159. EARP, 183. Edinger, 204. Egerton, 44. Einhorn, 122, 141. Ellinger, 150, 151. Elsmore, 156. Emmerling, 91, 153, 164. Empedocles, 27. Engler, 189. Eotvos, 183. Epicurus, 28. Erdmann, 133, 207. Erlenmeyer, 53, 88, 93, 102, 124, 128, 147, 150, 199, 221, 241. Esson, 194. Euler, 143. Eyde, 162, 245. FAHLBERG, 130, 241. Faraday, 3, 57, 77, 80, 89, 117, 121, 168, 174, 185, 215, 233, 23 4, 236. Farmes, 163. Favre, 191. Fehling, 123, 124, 144, 236. Fenton, 146, 201. Picks, 178. Figuier, 161. Firmicus, J., 6. Fischer, E., 113, 122, 128, 135, 140. 142, 144, 145, 146, 147, 148, 150, 151, 169, 199, 200, 204 226, 240, 241, 242, 243, 244. Fischer, O., 169, 240. Fittig, 93, 117, 118, 120, 122, 124 135, 221, 237, 238, 243. Fleck, 130, 243. "ontaine, 171. 'ourcroy, 19, 66, 137, 151, 213. 7orster, 102. 7ranchimont, 170. 7ranke, 65. Frankland, 52, 53, 83, 86, 88, 101, 117, 122, 124, 130, 166, 219, 236, 237. ?raunhofer, 187. ^remy, 62, 65, 200. 7resenius, 201, 202. Friedel, 67, 118, 119, 120, 130, 221, 239. ?riedrich, 173, 244. Friend, 55. Friedlander, 134. Freund, 94, 118, 121, 140, 141. Fritzsche, 125, 128, 235. Fuchs, 176. GADOLIN, 73, 175. Gahn, 62, 70. Gal, 200. Galvani, 49. Gamgee, 150. Garden, 93, 233. Gattermann, 72, 118, 121, 175, 200, 201, 227, 243. Gautier, 128. Gay-Lussac, 3, 33, 35, 36, 60, 62, 69, 71, 72, 73, 78, 79, 80, 86, 125, 157, 160, 161, 173, 175, 180, 182, 203, 204, 205, 213, 214, 218, 232, 233. Geber, 8, 28, 29, 62, 64, 65, 125, 209, 210. Geiger, 141. Geissler, 203. Gengembre, 71. Geoffrey, 45. Gerhardt, 37, 53, 81, 82, 83, 84, 85, 86, 87, 91, 102, 124, 130, 218, 220, 235, 236, 237. Gerlich, 146. Geuther, 101, 238. Gibbs, Wolcott, 68, 195, 240. Giesecke, 141, 233. Giesel, 75. Gilchrist, 156, Girard, 199, INDEX OF NAMES 251 Gladstone, 47, 143, 185, 216, 237. Glauber, 45, 62, 65, 73, 159, 168, 212. Glover, 160. Gmelin, 37, 150, 168, 233. Gnehm, 169. Goldschmidt, 109, no, 143, 158, 244. Gomberg, 119, 244. Gooch, 202. Goodyear, 166, 235. Gossage, 159. Grabe, 91, 93, 102, 131, 169, 170, 199, 200, 222, 239, 240. Graham, 61, 63, 82, 178, 191, 217, 234. 237, 238. Gray, 206, 207. Green, 205. Gregor, 69. Grier, 120. Griess, 96, in, 118, 128, 151, 169, 170, 200, 221, 238, 240. Grignard, 119, 121, 122, 124, 128, 130, 131, 142, 227, 244, 245. Groth, 176. Grotthus, 56. Guimet, 168. Guldberg, 47, 48, 180, 192, 239. Gustavson, 123, 200. Guthrie, 195. Guye, 113, 114, 173, 206, 207, 223, 242, 244. HAARMANN, 123. Haber, 191. Hadrich, 115. Haitinger, 75. Hall, 67. Haller, 114, 115, 143, 227, 243. Halliday, 161. Hampson, 22, 174, 24.3. Hansen, 72. Hantzsch, 71, 103, 1:0, in, 133, 178, 200, 205, 226, 227, 242, 243- Harcourt, 194. Hargreaves, 159, 243. Harries, 142, 143, 166. Hartley, 96, 104, 181, 187. Hartmann, 200. Hatchett, 70. Hatfield, 71. Hautefeuille, 193. Hauy, 66, 175. Heintz, 204. Helmholtz, 139, 191. Hemmelmayer, 92. Hemming, 159. Hempel, 205. Hendrixson, 193. Hennel, 121. Henrichsen, 184. Henry, 33, 54, 146, 183, 195, 205. Hepp, 169. Herapath, 173. Hermann, 123, 124. Herrmann, 102. Hermes Trismegistus, 7. Heroclitus, 27. Herschel, 112, 186. Hess, 190, 191, 235. Hesse, 141, 143, 234. Hessel, 175. Heumann, 169, 200. Hewitt, 187, 205, 244. Heydwiller, 178. Hilditch, 115, 130. Himly, 143. Hinsberg, 132, 134. Hittorff, 68, 177, 237. Hjelm, 70. Hjelt, 195. Hlasiwitz, 102, 120. Hobrecker, 132. Hobson, 102, 130. Hoffmann, 210. Hofmann, A. W., 84, 85, 86, 102, 106, 117, 120, 123, 127, 128, 129, 130, 141, 145, 146, 151, 168, 169, 170, 180, 199, 201, 219, 223, 236, 239, 240. Hollwachs, 182. Homberg, 14, 62, 69. Homer, 62. Hope, 69. Hopkins, 150. Horbaczewski, 151. Horstmann, 48, 96, 173, 182, 2l6. Howard, 162, 171. Howbres, 162. Hiibner, 132. Hunt, 156. 252 A SHORT HISTORY OF CHEMISTRY Hutchison, 162. Hypatia, 6, 8. IPATIEW, 143. Isay, 151. JACKSON, 121. Jacobi, 156. Jacobson, 101. Jager, 184. Jahns, 151, 186. James, 201. Japp, 92, 126. Jellet, 193. Jessup, 44. Jobst, 151. Johnson, 143. Jolly, 178. Jones, 115, 178. Jorgensen, 54, 55, 65, 140, 222. Joule, 172, 173, 191. Judson, 194. Jungfleisch, 193. KAHLENBERG, 178, 184. Kaiser, 162. Kalle, 130. Kamp, 189. Kane, 117, 118, 143, 235. Kannonikow, 142, 143. Kapfer, 203. Kast, 130. Kauffmann, 58, 187, 243. Kay, 85, 120, 143, 237. Kayser, 43, 186. Kehrmann, 106, 187. Kekute, 53, 82, 85, 86, 87, 88, 89, QO, 95, 96, 98, 99, 100, 108, in, 113, 117, 118, 122, 123, 125, 128, 129, 130, 143, 150, 170, 174, 192, 200, 220, 230, 239. Kellas, 106. Kellner, 158, 159, 241. Kelvin, Lord, 183, 191. Kestner, 125, 161, 233. Kiliani, 144, 146, 241. Kipping, 115, 116, 130, 227, 245. Kirchhoff, 69, 186, 237, 238. Kjeldahl, 150, 204, 241. Klages, 115. ( Klaproth, 66, 69, 70, 73, 125, 201, 202, 213, 231. Klinger, 54. Knap, 153, 165. Knietsch, 160. Knoblauch, 194. Knoevenagel, 99, 118, 126, 227. Knop, 150. Knorr, 92, 98, 102, 103, 104, 133, 135, 140, 141, 227, 243. Koch, 146. Kohler, 130. Kohlrausch, 177, 178, 182. Kolbe, 52,53, 83, 84, 117, n8, 122, 125, 127, 128, 130, 137, 150, 192, 201, 219, 236, 238, 240. Kondakow, 142. Konigs, 140, 141, 199. Koninck, 146. Konowalow, 196. Kopp, 174. 176, 182, 183, 190, 215, 236. Korner, 89, 91, 95, 96, 150, 221, 239, 240. Kossel, 150, 151, 241, 243. Kostanecki, St. Von, 91, 136, 170, 243- Kramer, 93. Kruger, 54, 143. Kriiss, 187. Kiihne, 139. Kundt, 22, 189. Kunkel, 7, n, 14, 29, 81, 210. Kuster, 105, 178. LAAR, 100, 104, 241. Ladenburg, 92, 95, 96, 97, 118, 130, 133, 134, !40, I41. I5ri 222, 239, 240, 242. Lampadius, 129, 201, 231. Landolt, 115, 129, 172, 183, 185, 2l6, 243. Laplace, 182, 190. Lapworth, 104, 105, 122, 244, 245. Lassaigne, 125, 203. Lautemann, 200. Laurent, August, 38, 52, 80, 81, 82, 84, 86, 93, 120, 123, 125, 140, 141, 168, 201, 218, 234, 235, 236. Lauroguais, 121. Lauth, 169. INDEX OF NAMES 253 Lavoisier, 3, u, ig, 20, 23, 24, 25, 26, 30, 31. 32, 50. 59. 60, 62, 63, 71, 76, 78, 137, 152, 166, 172, IQO, 202, 203, 205, 2IO, 211, 212, 230, 231. Lawrence, 122. Lawrie, 207. Le Bel, 108, 112, 113, 115, 125, 227, 240, 242. Leblanc, 159, 231. Lebrun, 167. Le Chatelier, 155, 165, 189, 193. Lecoq de Boisbaudran, 69, 73, 186, 217. Leduc, 179, 206. Lefebre, 162. Lehmann, 175, 242. Leidie, 65. Lellman, 193. Lemoine, 193. Le Rossignol, 107, 118, 130, 194, 200. Leser, 143. Letts, 92. Leuchs, 139, 153, 234. L£vy, 67. Lewkowitsch, 113. Libavius, 65, 120, 156. Liebermann, 93, 128, 141, 146, 169, 170, 201, 204, 221, 239. Liebig, 52, 61, 62, 63, 65, 77, 78, 79, 80, 82, 86, 102, 120, 121, 122, 123, 124, 125, 138, 139, 140, 141, 146, 147, 148, 150, 151, 152, 153, 171, 198, 200, 203, 204, 215, 218, 233, 234, 235, 236, 239. Liebreich, 92, 147, 151. Limpricht, 92, 150, 200, 204. Linde, 22, 174, 243. Linebarger, 179, 182. Lippmann, 188, 199. List, 143. Lister, 120, 239. Lob, 127, 244. Lobry de Bruyn, 71, 225. Lockyer, 22, 43, 186. Loew, 144, 242. Lorentz, 185, 241. Lorenz, 185, 241. Lorin, 199. Lessen, 54, 71, HI, 141, 182, 221, 240. Lowenherz, 193. Lowig, 129, 130. Lowry, 72, 104, 105, 245. Lucretius, 28. Ludwig, 139. Liilin, 113. Lully, 120. Lunge, 167, 200, 205. Luther, 188. MACDONALD, 130. Mackay, 162. Macquer, 164, 168. Magnus, 65, 121, 139. Mallerot, 161. Mallet, 207. Marcet, 151, 232. Marchand, 207. Marchlewski, 146, 244. Marckwald, 75, 114, 183, 208, 227, 244, 245. Marggraf, 62, 69, 156, 161, 186, 198, 201, 202, 210, 230. Margueritte, 65, 205. Mariotte, 172. Marignac, 42, 65, 72, 73, 191, 206, 207, 217. Markownikow, 94. Marshall, 72. Martin, 156. Martius, 169, 199. Matthey, 156. Mathesius, 203. Maxwell, 173, 186. Mayer, 146, 172, 189. Mayow, 13, 15, 17, 18, 19, 20, 25, 210, 229. McDougall, 162. McKenzie, 114, 124, 244. McMillan, no. Medicus, 151. Mehrer, 163. Meissheimer, 153. Meissner, 162. Melsens, 125. Mendius, 127. Mendelejew, 39, 41, 69, 70, 174, 177, 2x6. Menschutkin, 228. 254 A SHORT HISTORY OF CHEMISTRY Merck, 141, 236, 241. Merling, 141. Merz, 91. Messel, 200. Messinger, 203. Meyer, E. von, 51, 131. Meyer, Lothar, 30, 183, 200, 216. Meyer, R., 139, 187. Meyer, Victor, 92, 105, 106, 109, 113, 122, 127, 129, 180, 199, 228, 240, 241, 243. Michael, 126, 129, 130, 200. Michaelis, 115. Miller, 141, 186. Mitscherlich, 36,65, 68, 77, 84, 117, 121, 128, 130, 152, 170, 175, 176, 179, 206, 214, 233, 234, 235- Moore, 22. Mohr, 205. Moir, 44. Moissan, 67, 70, 71, 72, 158, 163, 225, 242, 243. Moldenhauer, 165. Mond, 159. Morin, 143, 164. Morley, 179. Morveau, Guyton de, 30, 159, 212, 231. Mosander, 67, 73. Miiller, 200. Mulliken, 192. Murdoch, 167, 231. Muspratt, 159, 170. NAPOLEON, 212. Natanson, 193. Nef, 153. Neilson, 156, 234. Nernst, 47, 178, 184, 191, 193, 195, 223. Neri, 163. Neuberg, 146. Neumann, 190, 237. Neville, 116, 245. Newberry, 165. Newlands, 39, 238. Newton, 46. Nicholson, 24, 231. Niemann, 141. Niepce, 188. Nietzski, 120, 169, 187, 199, 222, 241. Nilson, 69, 73, 180, 190, 207, 217. Nobel, 170, 171, 238. Nolting, 131, 199. Northmore, 174, 231. Noyes, 178, 194, 201. ODLING, 39, 52. Oersted, 141, 233. Ogier, 175. Olzewski, 174, 241. Onnes, 22, 174, 245. Ost, 91. Ostwald, 57, 177, 181, 182, 183, 187, 193, 194, 195, 223, 242. O'Sullivan, 153. Otto, 102, 130. Oudemans, 115. PAAL, 133. Palissy, 164. Paracelsus, 9, 29, 62, 65, 209. Parker, 158, 245. Parkes, 156. Parrot, 178. Pasteur, 112, 113, 152, 153, 176, 215, 237. Patterson, no, 115. Pattinson, 156. Payen, 153, 235. Peachey, 115, 116, 244. Pebal, 175. Pechiney, 158, 241. Pelletier, 140, 141, 151, 201, 233. PeUigot, 70, 71, 79, 120, 125, 200, 218, 234. Pelouze, 121, 124, 143, 164, 171, 218. Penny, 199. Personne, 200. Persoz, 153, 235. Perkin, A. G., 136, 169, 170, 205. Perkin, F. M., 202. Perkin, W. H., Sen., 91, 103, 122, 124, 125, 127, 135, 146, 150, 168, 169, 185, 200, 204, 22O, 237. 239, 240, 243. Perkin, W. H., Jun., 93, 94, 95, 118, 126, 141, 142, 143, 145, 228, 245- INDEX OF NAMES 255 Peters, 115. Petersen, 183, igo, igg. Petit, 36, i8g, igo, 206, 217, 233. Pettenkofer, 42, 138, 140. Pettersen, 180. Pfaff, 125. Pfeffer, 177, 178, 180, 240. Pfeiffer, 65, 131. Philips, 160. Piccard, i6g. Pictet, A., 140, 141, 245. Pictet, K., 174, 240. Pinner, 102, 106, 133, 141. Piria, 7g, 120, 123, 125, 146, 200, 204, 219, 235. Piutti, 150, 242. Planta, 141. Playfair, 157, 163. Pliny, 62, 168. Plucker, 184. Poggendorff, 233. Polis, 130. Ponomarew, 151. Pope, 115, 116, 17% 223, 244, 245. Posselt, 141, 234. Precht, 75. Priestley, 13, 16, 17, 18, 19, 20, 24, 25, 26, 62, 70, 71, 197, 202, 205, 211, 212, 230. Pringsheim, 138. Proust, 46, 49, 65, 120, 210, 212, 231, 232. Prout, 41, 42, 150, 214, 232, 233. Pschorr, 140, 141. Ptolemy Soter, 8. Purdie, 113, 114. RAMMELSBERG, 68. Ramsay, 20, 21, 22, 40, 55, 58, 71, 174, 180, 183, 186, 207, 223, 243, 244, 245. Raoult, 177, 181. Rayleigh, 20, 21, 173, 174, 179, 224, 243- Readman, 158, 245. Reaumur, 164, 204. Rebuffot, 165. Redtenbacher, 150. Reformatski, 122. Regnault, 81, 121, 140, 141, 174, 179, 189, 190, 215, 236. Reich, eg. Reicher, 196. Reimann, 141, 234. Reinsch, 120, 200. Reinitzer, 175. Remsen, 130, 241. Retgers, 175, 182. Rey, 17, 25, 172. Reynolds, 129, 207. Richards, 207. Richter, J. B., 32, 63, 211, 231. Richter, 69. Riecke, 186. Riedel, gi. Ris, 132. Ritter, 188. Ritthausen, 146. Reberts, 162. Robia, 164. Robiquet, 141, 153, 234. Rochleder, i6g. Rodger, 183. Rodziszewski, 132. Roebuck, 160, 230. Rohde, 141. Rome" de 1'Isle, 175. Romer, 165. Roosen, 151. Rose, G., 67. Rose, H., 46, 65, 70, 201, 202, 217. Rosenstiehl, i6g. Roscoe, 54, 62, 65, 70, 157, 186, 188, 207, 217. Rouelle, 13, 63, 128, 150, 210, 229, 230, Roussin, 127. Rowland, 186. Roozeboom, 195, 196. Riicker, 184. Rudolph , 92. Riidorff, 181. Ruff, 145, 146, 244. Riigheimer, 141, 241. Runge, 43, 75, 92, 120, 128, 168, 170, 186, 235. Rutherford, 13, 19, 70, 230. SABATIER, 118. Sabarejew, 179. Sachs, 138. Sachse, 100. 256 A SHORT HISTORY OF CHEMISTRY Salet, 175. Sand, 202. Sandmeyer, 200. Sattler, 168. Saussure, 137, 203. Sautter, 115. Saytzew, 124, 125, 130, 221. Scheele, 13, 16, 17, 18, 19, 20, 23, 25, 62, 64, 65, 66, 69, 70, 71, 76, 77, 92, 102, 120, 121, 123, 125, 151, 186, 188, 199, 201, 202, 211, 230, 231. Scheibler, 92, 146, 151, 239. Scherer, 145, 176, 237. Schiel, 82. Schiff, 96, 103, 134, 146, 204. Schimmel, 143, 161. Schlesmann, 193. Schlutius, 163. Schmidt, in, 143. Schorlemmer, 54, 169. Schonbein, 68, 72, 171, 199. Schotten, 204. Schraube, 111, 199. Schroder, 182. Schrotter, 141. Schryver, 107. Schultze, 150, 188. Schulze, 120, 238. Schunhardt, 62. Schurer, 168. Schutze, 187. Schiitzenburger, 72. Schutzenbach, 161. Schwald, 200. Schwann, 153, 235. Schwarz, 170. Schweizer, 143. Seebeck, 69. Seger, 164. Se"guin, 139, 231. Selmi, 147. Semmler, 142, 143. Senarmont, 67. Senderens, 118. Senebier, 137. Serullas, 121, 200, 234. Sertuerner, 139, 141, 233. Seubert, 207. Shenstone, 141. Shields, 183, 243. Siemens, 156, 164. Silber, 94. Silbermann, 191. Silow, 184. Silva, 1 20. Simpson, 121, 125. Skraup, 132, 134, 140, 141. Smiles, 71, 107, 116. 118, 130, 200. Sobrero, 121, 171, 236. Solomon, 5. Solvay, 159, 238. Sonnenschein, 140. Soret, 72. Soubeiran, 71, 121. Spilker, 93. Spode, 164. Sprengel, 182. Spring, 72. Staedel, 183. Stahl, 15, 16, 210. Staigmuller, 41. Stark, 58, 186. Stas, 42, 146, 199, 206, 207, 217, 235- Staudinger, 126. Stenhouse, 120. Stephen, 143. Stewart, 107, 126, 192, 196. St. Gilles, 47, 193, 238. St. Meyer, 184. Stohmann, 96. Stoney, Johnstone, 41, 44, 186. Streatfield, 126. Strecker, 124, 125, 128, 139, 141, 147, 148, 150, 151, 220, 237, 238. Stromeyer, 69, 156. Sudborough, 106. Swan, 186. Sylvius, 10, 14. Synesius, 8. TACHENIUS, 10, 201. Tafel, 135, 141. Talbot, 188. Tammann, 175, 180. Tanret, 145. Tennant, 70, 160. Tessie", 165. Tessorin, 178. Thales, 27. INDEX OF NAMES 257 Thdnard, 60, 62, 65, 71, 72, 84, 129, 157, 160, 168, 203, 214. Theophrastus, 69. Thiele, 54, 99, 100, 228, 244. Thole, 196. Thomas, 156. Thomsen, Julius, 47, 96, igi, 193, 216, 237. Thomson, Thomas, 41. Thomson, Sir J. J., 43, 56. Thorpe, 73, 183, 184, 207. Tickle, 244. Tiemann, 122, 123, 142, 143. Tilden, 142, 143, 190. Tilghman, 164. Tollens, 117, 126, 183, 199. Traube, J., 103, 177, 182. Traube, W., 149, 151, 244. Travers, 22, 244. Trouton, 183. Tschitschibabin, 119. Tschugaew, 114, 115, 224. ULRICH, 75. Unger, 151, 236. Unverdorben, 128, 233. Urbain, 73, 201. Ure, 171,234. VALENTINE, Basil, 9, 23, 29, 62, 64, 65, 69, 70, 120, 198, 201. Van der Plaats, 207. Van der Waals, 173, 179, 182, 206, 224, 241. Van Deventer, 196. Van Grote, 126. Van Helmont, 10, 17, 19, 20, 23, 62, 64. 65, 76, 117, 152, 170, 172, 202, 209. Van Than, 129, 239. Van 't Hoff, 48, 67, 94, 100, 108, no, 112, 113, 115, 125, 126, 177, 178, 180, 191, 194, 195, 196, 224, 240, 241. Varrentrapp, 203. Vaubel, 100. Vaudin, 161. Vauquelin, 66, 69, 70, 125, 137, 150, 213, 231, 232, 233. Veley, 205. Veraguth, 94, 245. 17 Verguin, 169, 237. Vernet, 181. Vernon, 184. Vieille, 171, 189, 242. Villiger, 143. Vogel, 187. Voget, 143. Voit, 138, 139. Volckel, 143. Volhard, 133, 150, 151, 205, 222, 239. Volta, 49, 178. Vongerichten, 141. Von Pechmann, 92, 118, 123, 127, 128, 228, 243. Von Reichenstein, 70. WAAGE, 47, 48, 192, 239. Wackenroder, 72. Wagemann, 161. Wagner, 142, 143, 157. Wanklyn, 169. Walden, 113, 114, 115, 177, 178, 184, 224, 243, 245. Walker, J. W., 178, 194. Walker, 41, 177, 192, 193, 224. Wallach, 142, 143, 228. Walz, 146. Warburg, 22, 189. Waterson, 173, 236. Watson, 70, 230. Weber, 71, 190. Wedgwood, 164. Weidel, 140. Weil, 132. Weith, 91, 102. Weldon, 158, 239, 241. Welsbach, 73, 158, 167, 241. Welter, 120, 169, 231. Weltner, 200. Wenzel, 45, 192, 230. Werner, 54, 55, 65, no, HI, 175, •*a*r 242. Wertheim, 129. Weselsky, 169, 201. Whiteley, 114. Whitney, 178. Wiedemann, 189. Wiggers, 143. Wiis, 178. Wilhelmy, 47, 153, 193, 194, 237. 258 A SHORT HISTORY OF CHEMISTRY Wildemann, 188. Wilsmore, 126, 192, 245. Will, 146, 203, 238. Willgerodt, 115. Williams, 143. Williamson, 52, 57, 84, 85, 86, 120, 121, 220, 237. Willstatter, 94, 138, 140, 141, 228, 244, 245. Winkelblech, 178. Winkler, 70, 160, 165, 205, 207, 217, 240. Winsor, 167. Wislicenus, J., 94, 109, 112,119, 122, 124, 125, 228, 240. Wislicenus, W., 71, 103, 104. Witt, 187. Wittorf, 143. Wohl, 145, 146, 243. Wolffenstein, 72. Woskresorski, 123, 151. Wolf, 126. Wolter, 165. Wohler, 3, 62, 65, 68, 69, 71, 72, 77, 78, 80, 86, 102, 120, 122, 123, 124, 125, 128, 130, 137, 139, 141, 146, 147, 150, 151, 157, 163, 197, 202, 2l8, 233, 234. Wollaston, 35, 70, 150, 186, 187, 213, 231, 232. Wray, 125. Wright, 141. Wroblewski, 95, 174, 241. Wurtz, 51, 52, 71, 73, 84, 85, 86, 92, Il8, 119, 122, 127, 151. 219, 236, 237, 239, 240. YOSHIDA, 143. Young, S., 174, 180, 224. Young, T., 182. ZEISE, 129. Zeisel, 141, 201, 204. Zelinsky, 94, 245. Zincke, 144, 241. Zinin, 127, 128, 170, 199, 219, 236. Zogoumenny, 199. Zosimos of Panopolis, 8. INDEX OF SUBJECTS ACETOACETIC ester, 101. Acetyl theory (Liebig), 79. Acid amides and anilides, organic, 124, 151. Acid anhydrides and peroxides, organic, 124. Acid chlorides, organic, 124. Acids, 13, 50, 59, 62, 71, 122-5, 145- 5i. — amido, detailed summary of, 114, 125, 145, 147, 150. — carboxylic, detailed summary of, 122, 125. — detailed summary of, 62, 71. — ethylenic, detailed summary of, 124, 125. — hydroxy, detailed summary of, 124, 125. — ketonic, detailed summary of, 126. — polybasicity of, 52, 61. Affinity, chemical, 45. — residual, 54. Agricultural chemistry, 138. Air, nature of, 16, 17. Albumens, 147. Alchemy, medicinal, 4, 7, 9. — transmutational, 4, 6, 7. Alcohols, detailed summary of, 119, 120. Alcohol, technical methods, 160, 161. Aldehydes, detailed summary of, 121, 123. Alexandrian Academy, the, 8. Alkalies, 64. — electrotechnical methods of preparation, 157, 158, 159. Alkaloids, detailed summary of, 119, 120. Allotropy, 68. Amido-compounds, organic, detailed summary of, 127, 128. Ammonium bases, organic (Hof- mann), 84, 85. Analysis, gas, 205. — inorganic qualitative, 201. quantitative, 201. — mineral, 66, 201. — of alkaloids, 140. — of sugar, 144. — organic qualitative, 202. quantitative, 203. — spectrum, 21, 68, 157. — volumetric, 204. Animal chemistry, 137. Antimony, organic derivatives of, 129. Apparatus, improvements in, 197, 198. Arabs, chemistry of, 8. Arsenic, organic derivatives of, 129. Atom, definition of (Laurent), 38, 81. Atomic theory (Dalton), 32-4. — weight confusion (1830-1850), — weights, determination of (Berzelius), 35, 206. (Cannizzaro), 38, 206. (Dumas and Marignac), 206. (modern), 206-7. (Stas), 42. (summary), 207. mathematical regularities in, 42-4. " BARRED SYMBOLS " (Berzelius), 31. Bases, 13, 50, 52. 260 A SHORT HISTORY OF CHEMISTRY Bases, detailed summary of, 64. Benzene, physical properties of, 96. — space formula for (dynamic), 98, 100. (static), 97, 99, 100. — theory, 88-90, 94-6, 113. Boiling-point, 183, 184. elevation of (Beckmann), 181. CARBIDES, 163. Carbon atom, tetrahedral (Le Bel- van't Hoff), 108, 112. Carbonic acid, Black on, 18, 64. nature of, 19, 62. Catalysis, 194. Cathode rays, 43. Cements, 164, 165. Chemical methods, improvements in, 198-201. Chemical statics and dynamics, 48, 192-5. Chemistry, origin of name, 6. Chinese, chemistry of, i, 3, 5. Chlorine, elementary nature of, 60. — technical preparation of, 158. Christianity in relation to chemistry, 6, 8, 9. Classification of organic compounds (Gerhardt, Laurent), 82, 86. Clays, 164. Coal-tar products, 167, 168. Colloids, 178, 179. Colour, theories of, 187. Combustion and respiration, analogy between, 14. — Lavoisier's theory of, 3, 24, 26, 166. — phlogistic theory of, 2, 12, 15, 16. Condensation, aldol, 122. — benzoin, 122. — Claisen, 122. — Knoevenagel's, 126, — of malonic and acetoacetic esters, 126. — Michael's, 126. Constant combining proportions, law of, 46, 49. Controversy, Proust-Berthollet, 46. Copulated compounds, 82, 83. Critical phenomena of gases and liquids, 174. Crystallography, 66, 175. Crystals, liquid, 175. Cyclic compounds, conjugated car- bocyclic, detailed summary of, 93- heterocyclic, detailed sum- mary of, 91, 92, 131-6. reduced carbocyclic, detailed summary of, 94, 118. DESMOTROPY, 101. Diazo-compounds, detailed summary of, 128. isomeric, in. Dielectric constant, 184. Diffusion, 178. Diketones, detailed summary of, 123. Dispersive power, 185. Dissociation, 174, 175. Dyestuffs, 5, 167. — detailed summary of, 168-70. EGYPTIANS, chemistry of, 2, 3, 5. Electrical conductivity, 177, 178. of acids, 177. of pure water, 177. Electric furnace, 158. Electrochemical theory of Arrhenius and Faraday, 57. (dualistic) of Berzelius, 31, 50, 51, 56, 60, 61, 63, 66. of Clausius, 56. (dualistic) of Davy and Volta, 49, 56, 76. of Grotthus, 56. Electrochemistry, theories of, 191, 192. Electrolysis, hydrate theory of, 58. — laws of, 51. Electrolytes, amphoteric, 178. Electronic theory, 44, 56, 58. Electrons, 43. Electrotechnical methods, 154, 156, 157, 158, 159, 162, 163. Elements, alchemical, 14, 28. — Aristotelian, 14, 27. — Boyle's definition of, 29, 32. — detailed summary of, 69, 70. Enzymes and enzyme action, 152. INDEX OF SUBJECTS 261 Epochs, chief chemical, i. Equivalent combining proportions, law of, 32. — definition of (Laurent), 38, 52, 81. Esterification, 47, 193. Esters, detailed summary of, 121. Ether and alcohol, relation between (Williamson), 84. Etherin theory (Dumas and Boullay), 79- Ethers, detailed summary of, 119. Ethylenic compounds, stereoiso- meric, 109. Eutectic point, 196. Explosives, 170, 171. FERMENTATION, theories of, 152, Fluorescence, 187. Freezing-point, depression of (Raoult), 181. Furfurane compounds, 92, 133, 136. GASES, for heating purposes, 166. — liquefaction of, 21, 174. — • physical investigation of, 13, 172-4. — the inert, 20, 2,1, 40. Gas-lighting, technical improve- ments in, 158, 167. Glass, 5, 163. Glucosides, 142, 146. Greeks, chemistry of, 2, 6. Grignard's reaction, 119, 121, 122, HALIDES of non-metallic elements, 72. Halogens, 60. — compounds, organic, 200. Heat of chemical combination, 190. — technical methods, 166. Hemihedry, 176. Hindus, chemistry of, i, 5. Hydrazine derivatives, detailed summary of, 128. Hydrides of the elements, 71. -- nitrogen group, 71. Hydrocarbons, detailed summary of, 117. Hydrogen, nature of, 23, 24. Hydrolysis, 193, 200. Hygienic chemistry, 138. Hypothesis, Avogadro's, 35, 173. — Prout's, 41. ILLUMINANTS, 166. India rubber industry, 165. Indicators, theory of, 205. Inductive reasoning, applied to chemistry, 2, n, 12. Inorganic compounds, structure of, 49- Internal friction, 183, 196. Ionic theory of Arrhenius, 57, 61. Isomerism, 68, 77. — dynamic, 100-5. — geometrical, 107-11. — optical, 111-16. Isomorphism, Mitscherlich's law of, 49. Isonitriles, detailed summary of, 128. Isonitroso compounds, detailed summary of, 129. Isoquinoline compounds, 135, 136. JEWS, chemistry of, 3. KETEN, 126. Ketones, detailed summary of, 121, 123. Kinetic theory of gases, 173. LATENT heat, 190. MAGNETIC rotation, 185, 186. Magnetism, 184. Mass-action, law of, 45, 47, 48. Matches, 165. Melting-point, 183. Meta elements (Crookes), 73. Metal alkyls, detailed summary of, 130. Metallammine compounds, 54. Metallurgy, 5, 154-6. Metallurgy of iron and steel, 155-7. Metals of the rare earths, 73. Meteorites, 68. Mineralogy, 65. Molecular dispersive and refractive power, 96, 103, 185, 193. 262 A SHORT HISTORY OF CHEMISTRY Molecular magnetic rotatory power, 103, 185, 186. — volume, 96, 182. — weight, physical determination of, 179-81. Molecule and molecular weight, de- finitions of (Laurent), 38, 81. Morphotropy, 176. Multiple combining proportions, law of, 33, 49. NlTRILES, 124. Nitro and nitroso compounds, organic, 127, 171, 199. Nitrogen, discovery of, 19. — fixation of atmospheric, 155, 162, 163. — optically active, 115. — technical preparation of, 158. Nomenclature of chemical com- pounds, 30, 60. Notation, chemical (Berzelius), 31, 32. (Dalton), 32. — modern structure, 53, 87, 88. Nucleus theory (Laurent), 80. OCTAVES, law of (Newlands), 39. Optical activity and ring- formation, 114. — and unsaturation, 115. — of electrolytes, 115. — of homologous series, 114. — quantitative theory, 113. Organic chemistry, 13, 76, 117, 137. Osmotic pressure, 177. measurement of, 180, 181. Oxidation, electrolytic, 192. — of organic compounds, 199. Oxides and oxy-acids of nitrogen, phosphorus and sulphur, 71. Oximes, detailed summary of, 129. — stereo-isomeric, 109, no. Oxygen, discovery of, 18. — technical preparation of, 158. PAPER, 165. Periodic system of elements, 38-41, 53- anomalies of, 40, 208. (Benedicks), 74. Peroxide of hydrogen and per- acids, 72. Phase rule, 195. Phenols, detailed summary of, 120. Phlogistic chemists, 12. Phoenicians, chemistry of, 3, 5. Phosphorus, organic compounds of, 129. Photo-chemistry, 187-189. Physical properties, additive, con- stitutive, colligative, 181. and chemical constitution, relations between (electrical), 184. (mechanical), 181-4. — (optical), 185-189. (thermal), 189-91. Polyketides, 126. Polymerism, 68, 77. Polymorphism, 68, 176. Pottery, 5, 154, 164. Proteins, 145, 148. Purines, 145, 149, 151. Pyridine compounds, 91, 133, 134, 136. Pyrone compounds, 91, 136, 170. Pyrrol compounds, 92, 133, 136. QUADRIVALENCY of carbon, 87. Quinoline compounds/gi, 132-4, 136. Quinones, detailed summary of, 123. RADICLE theories in organic chemistry, 78, 83, 86. — theory, Liebig's first, 78. Radioactive elements, 75. Radioactivity, 23. Rate of reaction, 193, 194. Reduction of organic compounds, 118, 199. Reduction, electrolytic, 191. Refractive power, 185. Romans, chemistry of, 6. SALTS, inorganic, 13, 32, 50, 62, 63. Salts, inorganic, detailed summary of, 64, 65. Saturation capacity, 86. Selenium, optically active, 116. Silicon compounds, organic, detailed summary of, 130. INDEX OF SUBJECTS 263 Silicon, optically active, 116. Soap, manufacture of, 162. Societies, alchemical, 10. Soda manufacture, 159. Solution, theories of, 176, 177. Specific atomic heat, 36, 189. Specific gravity and specific volume, 182. Specific heat of gases, 189. of elements and compounds, 189, 190. Spectra absorption, 96, 104, 187, 193, 196. — of elements, 43, 186. Spectroscopy, 186, 187. Steric hindrance, 105-7. Structural theory, modern, in or- ganic chemistry, 78, 86, 87. Substitution, 51, 80, 166. Sugars, 142, 144, 146. — technical preparation of, 161. Sulphonation and sulphination, 200. Sulphur, optically active, 116. Sulphur compounds, organic, de- tailed summary of, 129, 130. Sulphuric acid, manufacture of, 155, 160. Surface tension, 182. Synthesis, asymmetric, 114. — electric, 192. — of alkaloids, 140, 141. — of amido-acids and proteins, 147, 148, 150. — of hydrocarbons, 118. — of organic dyestuffs (technical), 155- — of purines, 149, 151. - of sugars, 144, 146. — of terpenes, 142, 143. — of vegetable and animal pro- ducts, 139. TAUTOMERIC compounds, detailed summary of, 102, 103. Tautomerides, physical properties of, 103, 104. Tautomerism, 100. — theories of, 104, 105. Technical chemistry, 13. Terpenes, detailed summary of, 140, 142, 143. — technical preparation of, 161. Theory of residues (Gerhardt), 81. Thermite process (Goldschmidt), 158. Thermo-chemistry, 96, 189-91, 193. — of explosives, 170. Thiophene compounds, 92, 133, 136. Tin, optically active, 116. Transmutation of metals, 2, 5. Type theories in organic chemistry, 52, 78, 80, 84, 86. Type theory, mechanical (Dumas), 81. Types, four general (Gerhardt), 82, 86. Types, mixed (Williamson), 85, 86. UNSATURATION, conjugated, 54. Urea, derivatives of, detailed sum- mary, 128, 150, 151. VALENCY, 51-6, 85, 86, 88. — and the electronic theory, 56. — "normal" and "contra," 55. — Werner's theory, 54. Vapour-density determination (Du- mas), 37, 179- Hofmann), 180. Victor Meyer), 180. Regnault, etc.), 179. — — theory, 179. Vapour-pressure curves, 196. Vegetable chemistry, 137. Vinegar, manufacture of, 161. Vital force theory of organic chemistry, 77. Volumes, Gay-Lussac's law of, 33, 35. 173. WALDEN inversion, 113. Water, nature of, 16, 23,24. 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